Spatial Knowledge Navigation for the World Wide Web
By
William T. Neveitt B.S., M.Eng. Electrical Engineering and Computer Science (1996) Massachusetts Institute of Technology
Submitted to the Department of Electrical Engineering and Computer Science in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Computer Science
at the
Massachusetts Institute of Technology September 2000
@2000 Massachusetts Institute of Technology All Rights Reserved
Signature of Author:______Depaitment of Electrical Engineering and Computer Science September 7, 2000
Certified t Randall Davis Professor of Computer Science Thesis Supervisor
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Certified by: Seth Teller Professorof Computer Science Reader
Accepted by: 4rthur C. Smith Chairman, Committee on Graduate Students Department of Electrical Engineering and Computer Science
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The images contained in this document are of the best quality available. Spatial Knowledge Navigation for the World Wide Web
By William Neveitt
Submitted to the Department of Electrical Engineering and Computer Science On September 7, 2000 in partial fulfillment of the Requirements for the Degree of Doctor of Philosophy in Electrical Engineering and Computer Science
ABSTRACT Navigation is a fundamental but relatively underdeveloped method of information access. This thesis argues that a spatial metaphor can significantly enhance the navigability of a broad class of information spaces. Whereas previous efforts in information visualization have focused on increasing the amount of information available on the display, this thesis begins with the premise that there is far too much information to be seen all at once. To facilitate navigation, information architecture must help an end-user construct a working mental model of information that extends beyond the margins of the current view.
I define the knowledge navigation problem and outline five specific criteria for its solution. I then survey the practice of hypertext design, identify several recurring navigation pathologies, and argue that these pathologies stem from a basic mismatch between the physical organization of a hypertext and a user's perception of it as viewed through a page-centered browser. As an alternative, I review a design framework based on elements from urban architecture including landmarks, regions, paths, direction, and proximity (LRPDP) and argue that these elements can improve the navigability of information architectures.
To illustrate how the LRPDP elements can be applied in practice, I performed four case-studies: designing a citation database for machine vision, an on-line help system for software troubleshooting, a virtual dinosaur exhibit, and a digital research notebook for brainstorming. To evaluate the impact of a spatial view and of LRPDP design on navigability, I performed a series of usability studies. The results suggest that users explore more, remember more, and find more
2 answers to questions when provided with a spatial view of an information space. Further, subjects state their position more accurately, return to a known location more efficiently, and reorient more effectively when landmarks, regions, and paths are present.
I distill lessons from the case studies and the usability experiments down to a collection of simple design principles for future information architects.
Thesis Supervisor: Randall Davis Title: Professor of Computer Science
3 Table of Contents
Spatial Knowledge Navigation for the World Wide Web...... 1 Table of Contents ...... 4 Acknowledgements...... 6 Overview...... 8 The Knowledge Navigation Problem...... 10 IN TRO D U CTIO N ...... 10 THE WEB REVOLUTION IS BEGINNING ...... 10 THE USABILITY DEFICIT IS A GROWING CHALLENGE ...... 12 INFORMATION ARCHITECTURE CAN NARROW THE USABILITY DEFICIT ...... 13 EFFECTIVE INFORMATION SPACES SUPPORT THE CREATION OF A MENTAL MODEL ...... 14 QUERY AND NAVIGATE ARE COMPLEMENTARY ACCESS PARADIGMS...... 15 THE KNOWLEDGE NAVIGATION PROBLEM...... 17
DIGEST OF PREVIOUS WORK ...... 20 Navigation in Hvpertext ...... 22 O V ERV IEW ...... 22 PERCEIVING THE WEB...... 22
HYPERTEXT NAVIGATION PATHOLOGIES...... 25
DIAGNOSING HYPERTEXT NAVIGATION...... 34
DIGEST OF PREVIOUS WORK ...... 35 The Spatial Metaphor...... 37
IN TROD U CTIO N ...... 37 WHAT IS THE SPATIAL METAPHOR? ...... 37
INSIDE THE SPATIAL METAPHOR ...... 39
LRPDP: A COLLECTION OF SPATIAL DESIGN ELEMENTS...... 42 Case-Studies in Information Architecture...... 46 IN TR ODU CTIO N ...... 46
A SIMPLE 2D OVERHEAD PRESENTATION TECHNIQUE...... 46
WHEN IS SPACE USEFUL 9...... 47 EXPLORING THE EVOLUTION OF IDEAS IN THE MIT VISION SPACE ...... 49
TROUBLESHOOTING IN THE MICROSOFT OUTLOOK HELP SPACE...... 52
LEARNING ABOUT DINOSAURS IN THE VIRTUAL DINOSAUR EXHIBIT ...... 58 SENSE-MAKING IN THE THINKUBATOR ...... 60
4 CONCLUSION ...... 67 Usability Studies in Spatial Navi ation ...... 68 INTRODUCTION ...... 68 THE DIGITAL LIBRARIAN EXPERIMENT ...... 68 THE APERTURE EXPERIMENTS ...... 91 EXPERIMENT 1: ESTIMATING CURRENT LOCATION ...... 96 EXPERIMENT 2: RETURNING TO A LANDMARK ...... 100 EXPERIMENT 3: RE-ORIENTING...... 103 LESSONS FROM THE A PERTURE EXPERIMENTS...... 104 Design Principles...... 108 Future W ork ...... 112 Experim ent Instructions...... 114 M aps From the Librarian Experim ent ...... 119 Biblio raphv...... 131
5 Acknowledgements
Research is the art of seeing what everyone else has seen, and doing what no one else has done. - Anonymous
That's the nature of research--you don't know what in hell you're doing. - Doc Edgerton
I've come to realize that the first privilege of an MIT graduate education is the freedom to fumble gloriously though the wilds of research with students of the highest caliber and to laugh and learn together over a pint at the Muddy Charles. Cheers to Joanna Bryson, Mark Foltz, Michael De La Mazza, Sajit Rao, Lukas Rueker, Push Singh, Rebecca Xiong, and Deniz Yuret.
The second privilege of an MIT graduate education is the right to be humbled by the finest minds, to sit at their feet for a short while and to experience a small measure of their knowledge and wisdom. Many thanks to Seth Teller helping me to see that good ideas contain far too much information to be seen from a single point of view. Many thanks to Whitman Richards for helping me to build the mental model needed to stage and execute a logical experiment.
Special thanks to Patrick Winston, who taught me the meaning of good taste in big ideas by example, that verbs are the life of a sentence, that anthropology is the secret to understanding business, and most of all, that clarity of thought and action are the highest virtues of a thinking person.
Finally, very special thanks to my advisor, Randy Davis, for simply being the finest mentor any student could have. More than a towering intellect and a formidable debater, he is a consummate professional and the best listener I have ever known. His excellence is a lasting personal landmark for me and I will always cherish the unwavering support and patience he offered throughout this research.
6 For Mom and Kristy, who have always lit the way
7 Overview
The Problem: The World Wide Web is placing the sum of human knowledge within reach of the average household desktop. However, today's Web expands opportunistically rather than by design, driven more by the rapid advance of new technologies rather than the needs and limitations of the end-user. New design techniques are needed to bridge the widening gap between how fast information can be delivered and how fast information can be understood.
Navigation is an important but relatively under-developed method for information access. While a large community of researchers is working to improve query-based methods for information access, these methods fail to support a broad range of user activities because users either don't know what's available, don't know what they want, or don't know how to ask for it. In addition, although most supporting technologies for the Web have improved significantly in the past decade, the classical navigation interface - a page-centered browser - has remained virtually unchanged.
The Thesis: I argue that a spatial metaphor can significantly enhance the navigability of a broad class of information spaces. In particular, I provide a principled framework for design by showing how augmenting pages and links with spatial representational elements such as landmark, path, region, direction, and proximity (LRPDP) can improve navigability.
The Contributions: Five CriteriaforNavigability I define the navigation problem and outline criteria for its solution. Though a modest contribution, research in this area is early enough that there appears to be neither a widely accepted definition of navigation nor an operational list of criteria for its solution.
Problems with Hypertext Navigation and PotentialAdvantages of a SpatialMetaphor I survey the practice of hypertext design and identify several recurring navigation pathologies. I argue that these pathologies stem from a basic mismatch between the physical organization of a site and a user's perception of it as viewed through a page-centered browser. These problems
8 suggest that a spatial metaphor can improve navigation by making a familiar set of choices available in every view of the space, by providing a context for decision making that extends beyond the margins of the current page, and by separating where a user is from how the user got there.
Four Case Studies Illustrate the Design Approach I present four case-studies in spatial information architecture: a citation space of machine vision research at the MIT Al Lab, an on-line help space for Microsoft Outlook, a virtual museum exhibit on dinosaurs, and a digital research notebook called the Thinkubator. Each of these case studies demonstrates how a class of user activity can be reduced to a navigation problem and how the LRPDP elements can be applied in its solution. In addition, a set of tests is proposed to help determine whether or not a spatial metaphor is appropriate to a particular information space.
The DigitalLibrarian Experiment Evaluates the Impact of a Spatial View I present a usability study in which subjects were asked to pretend to be librarians for a Web site. Subjects were asked to freely browse the site for 15 minutes, to create a map of the site from memory, and to locate the answers to questions. Subjects in the first group were given a standard hypertext browser. Subjects in the second group were given a standard browser augmented with a spatial view. Spatial subjects demonstrated a strong preference to navigate in space and explored significantly more of the site. In the mapping task, spatial subjects reproduced more of the site. In the way finding task, spatial navigators successfully found the answers to more questions than their non-spatial counterparts.
The Aperture Experiments Evaluate the Impact of Landmarks, Regions, and Paths I present a series of simple experiments in which subjects were asked to perform representative navigation tasks in worlds with and without landmarks, regions, and paths. The results verify that users can state their position more accurately, return to a familiar location more efficiently, and reorient themselves faster in an aperture-limited world when landmarks, regions, and paths are present.
A Guidebookfor Design I distill lessons from the case studies and the usability experiments into a collection of tests, prescriptions, and hints for designers.
9 Chapter 1
The Knowledge Navigation Problem
Where is the wisdom we have lost in knowledge? Where is the knowledge we have lost in information? - T. S. Elliot
Introduction
Knowledge navigation is the process of accessing information within a larger collection by selecting a series of choices. As the scale and scope of digital information spaces such as the World Wide Web continue to expand, improved support for navigation is becoming essential. However, the challenges of knowledge navigation are poorly understood and relatively little work has been done to advance a design framework. I argue that today's Web is driven largely by the rapid growth of new technologies rather than the needs and limitations of the end-user. One consequence is a widening usability deficit that is replacing limited computational resources as the primary obstacle to the Web's development. Information Architecture is a new design field that is beginning to bridge this usability deficit. I survey the two primary access models of contemporary Information Architecture - query and navigate - and contrast their underlying assumptions. Lastly, I specify the Knowledge Navigation problem and propose criteria for its solution.
The Web Revolution is Beginning
The World Wide Web is placing the sum of human knowledge within reach of the average household desktop. The capture of disparate information fragments into the purview of a single screen is empowering everyday users to think and act at an unprecedented scale. Historians of science have compared the Web's impact to that of the printing press and foresee a new Information Age that will rival the significance of the Industrial Revolution [Robsn98]. Economists cite the productivity gains achieved through Internet technologies as a prominent factor in the prolonged inflation-free growth of the 'New Economy' period'. The business world is embracing the Web as the lynchpin of a new kind of corporate organizational structure [Orgzn].
I'To Boldly Go...', The Economist, March 25,2000
10 Virtually every corner of human endeavor, from intellectual property to comic strips, is being re- invented.
As of August 2000, the Web contains over 1 billion pages distributed across over 17 million sites [HobIT]. Every day, the web grows by about a million pages and roughly 600GB of text changes every month [HypSh99]. The number of pages, web servers, and network packets has been growing exponentially for almost a decade [HobIT]; the current doubling period for total sites is under 6 months. Although this explosive pattern of growth appears to be slowing, processing power and memory capacity continue to keep pace with Moore's Law, heralding a future in which computation is free and information spaces are larger, more connected, and more ubiquitous than ever before.
Web Growth
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Figure 1 - The growth of web sites from 1993 to present
Although the Web's growth has been stunning, estimates suggest that fewer than 30% of all U.S. residents use the Web on a regular basis and worldwide figures are substantially lower2 . Ample
2 Financial Times, October 8, 1999
11 headroom for continued growth implies that impact of the Web on our daily lives is just beginning to be felt.
The Usability Deficit is a Growing Challenge
The popularity of the Web has created an interesting practical problem. Although impressive strides have been made in the Web's underlying transport and processing technologies, these advances have not been matched by equally impressive improvements in the Web's usability. The result is a usability deficit - a widening gap between how much information can be delivered and how much information an end-user can assimilate. From the vantage of an inexperienced user, the usability deficit manifests itself in several ways:
Lack of Global Structure: Where does one start to browse the Web? Although individual sites may be coherently organized, there is little or no organizational infrastructure for the collection as a whole. As such, the Web resembles a mile-high pile of books rather than a well-kept library. Library science has evolved organizational standards such as the Dewey Decimal System and the Library of Congress classification scheme, but web sites are subject to the vagaries of designers with dramatically different experience, goals, and tastes. Once consequence for the end-user is that there is no consistent, reliable way to access related sites.
Lack of Local Structure: Users browse the Web by following hyperlinks to pages containing information and additional links. Yet the classical browsing interface has remained virtually unchanged since its inception almost a decade ago: disjoint, near-sighted, single page views with no supporting representation for the relationship between successive pages or for the larger context in which the current page resides. One consequence is that users can become disoriented or 'Lost in Hyperspace' [Edwds93].
Irrelevance: Query by keyword search is a very popular access method. However, because most keyword engines are based on superficial features of the underlying free text, query results are often replete with irrelevant matches.
12 The principal source of the usability deficit is becoming clear: the design of today's Web has been driven bottom-up by technology rather than top-down by the needs and limitations of the end-user. Ten years ago, providing higher bandwidth to the end users display was the key challenge. In the next ten years, as rapidly improving technology continues to diverge from a slowly improving interface, the key challenge will be bridging a much larger gap between the user's screen and the user's understanding.
Information Architecture Can Narrow The Usability Deficit
The navigation 3 problem resides in the larger setting of Information Architecture. The aim of an information architect is to organize a raw mass of data into a rational information space:
Information Space - an organized collection of data supporting a human activity
Information Architect - a designer of information spaces
To understand the challenges an information architect faces, it is instructive to consider how improvements in underlying technologies can turn an initially simple and useful information space into a barely usable artifact.
A Rolodex is a very simple information space. The data are contact information, the activity is finding a phone number or email address, and the organization is typically alphabetical ordering by last name. Useful information spaces like the Rolodex are pervasive in modem society; a course curriculum, your TV guide, a file system for your personal computer, a portfolio of vacation packages, a museum, and an atlas are all familiar and widely used information spaces.
New technologies are amplifying both the scale and scope of information spaces. Yesterday's Rolodex has been replaced by software that can run on a computer that fits in your pocket. Today, you can organize your contacts by name, business, geographical location, or birthday. You can search by keyword or by browsing a list. Your available storage space doubles roughly every two years. The information space you use to manage your contacts may be integrated with an email system that allows you to communicate with other users and associate threads of discussion with
' Hereafter, I will use the word 'navigation' to imply navigation in an electronic world.
13 each contact. Falling computing costs foreshadow information spaces that are much larger, more feature rich, and more widely used than ever before.
As the complexity of an information space grows, organizing it becomes more difficult. Tomorrow, the software Rolodex in your pocket may be embedded in a personal digital assistant and closely integrated with a wireless, worldwide network of contact information. Your Rolodex may be able to tell you why someone cannot be reached (perhaps they are on vacation), may let you know that an old friend is in the area, and may even start suggesting new people you should talk to. How will inexperienced users manage the impressive range of information and capabilities provided by pocket digital assistants without being overwhelmed?
The burden of unmanaged complexity ultimately falls upon the end user. When the Rolodex was first sold, an average person could probably completely understand how to use it in minutes. In the future, many users may need personal instruction just to retrieve a phone number.
The first premise of this research is the belief that organizing very complex information spaces such as the World Wide Web will demand a principled approach to design that begins by acknowledging the needs and limitations of the end-user. The second premise is the belief that the headlong rush of new technologies has left the importance of usability largely ignored.
Effective Information Spaces Support the Creation of a Mental Model
How can we better represent the requirements of the end-user in the design of tomorrow's information spaces? In order to use any artifact effectively, a user needs to build a basic understanding of its purpose, to recognize the available choices, and to predict the consequences these choices entail [Normn9O]. For example, using a pair of scissors requires understanding that they are used for cutting, that available choices include whether to open or close the blades and what to place between them, and that one may use the device by grasping the scissors with your fingers and squeezing. I will call a user's internal representation of a designed artifact a mental model:
Mental Model - An internal representation of a designed artifact used as the basis for making decisions. Elements of a mental model include an artifact's purpose, available choices, causal
14 relationships between states of the artifact, and mappings from a user's goal to the available choices.
Growing complexity makes it very difficult for users to construct a working mental model of an information space. Complexity arises from expanding scale, which implies that more items are made available: what new choices do I have and how are they related to my goal? Complexity also arises from expanding scope, which implies that the same information can be manipulated in new ways: what does this artifact enable me to do?
Supporting the creation of a working mental model is essential to successful design. What methods do contemporary information architects employ to help users construct a working mental model of an information space and what is the scope of their application?
Query and Navigate are Complementary Access Paradigms
The dominant access paradigms for today's information spaces are query and navigate. In the query approach, users specify terms or phrases describing information of interest and receive matches ranked by relevance. From the perspective of an end-user, the mental model for a query- based interface is exceptionally simple: describe your topic of interest and scan the returned list of results.
Speed and scalability have made query-based interfaces the method of choice for many portal sites on the Web [Excte], [AltVs], [WebCr], [Googl]. However, because matching is based largely on superficial features of text rather than the underlying meaning of documents, query results often contain thousands of irrelevant hits. More fundamentally, the query paradigm rests upon three implicit assumptions: 1. Knowledge of Extent - Users have working knowledge of what's available 2. Clarity of Purpose - Users know what they want 3. Facility with Vocabulary - Users know how to ask for what they want These three assumptions are often false. First, users don't always know what's available in a particular information space. For example, the most important paper to read in an on-line bibliographic database may be the one you have never heard of. Without a basic notion of what's there, a user cannot begin to ask for it. Second, users don't always know what they want. Even if they have a firm understanding of what's available, users may want simply to browse alternatives; for example, consider purchasing a gift for a friend through an on-line store. Finally,
15 users don't always know how to ask for what they want, event if they know what it is. The difficulties novice users have forming Boolean predicates for keyword search are a well-known example.4 In addition, special terminology may be required to search effectively. A user may know they are interested in mutual funds that have performed well recently, but may fail in their search simply because they have no idea what 'NAV' means (net asset value). Even if a perfect query engine could be built, the fact that many garden-variety access tasks violate the three query assumptions implies that access by query alone is insufficient.
The navigation approach enables users to take incremental steps towards information of interest by following hyperlinks. Yahoo is the most visible champion of access by navigation [Yahoo]. Because navigators identify items of interest by responding to options rather than generating descriptions, navigators need a richer mental model of the information space. The nature of this mental model will be examined in detail later in this chapter.
The navigation approach is less restrictive than the query approach because navigation does not require users to know what's available, what they want, or how to ask for it. Navigation requires only: 1. Ability to Choose - Users can accurately identify the available choices and decide what choice to follow next Unfortunately, constructing an information space that facilitates accurate choices is currently an intensive manual design exercise, and is therefore impractical at very large scales. Although scalability is a critical concern for Information Architecture, this thesis will concentrate on the properties effective information spaces ought to have rather than the methods information architects might use to construct them. Clearly, such properties are instrumental to the design and evaluation of fully automated approaches.
A large research community is working to improve query-based interfaces to the Web [HypSh99], [ShDepOO]. Surprisingly, although support for navigation has been considered to be one of the most important concerns for the future of the Web [GVUSu, see October 1997], navigation has received surprisingly little attention [NavEW97].
4 See Jacob Nielsen's Alertbox on Search Usability at http://www.useit.com/alertbox/9707b.html.
16 The Knowledge Navigation Problem
What does it mean to navigate in an electronic world? A first step towards this question must acknowledge that navigation is a "suitcase word"; not a singular concept, but a convenient bundle for several tangled notions. For example, an early workshop on the navigation problem asked several participants to submit their definitions of navigation prior to arrival [JulFu97]. Some of the responses included:
Navigation is ... aboutfinding your way confidently and successfully to your goal while discoveringfresh delights along the way.
-- Mark Apperley
Navigation is the cognitive process of acquiring knowledge about a space, strategiesfor moving through space, and changing one's meta-knowledge about a space.
-- Laura Leventhal
Navigation = Wayfinding + Locomotion; "Knowing where to go" + "Getting there". -- Rudy Darken
Navigation is getting lost. -- Jock Mackinlay
From these definitions and others like them, the inner structure of the navigation problem can begin to be seen. Navigation includes a user's goal:findinga specific item or acquiring knowledge of the overall character of an information space. Navigation also includes the means by which users pursue a goal: generating a novel path through a space, recalling afamiliarroute, using signs to guess where items may be located, or building a mental image of the organization. In addition, these definitions offer an instructive perspective on the present status of navigation research: navigation is complex and under-developed enough that even leading researchers in the field disagree on its basic defmition.
This thesis will focus on the mental models underlying navigation in electronic worlds. As such, I will rely on the following defmition throughout this thesis:
17 Knowledge navigation is the process of accessing information within a larger collection by selecting a series of choices
This definition derives from a computational view of navigation proposed by Furans [Furns97]. A more formal rendering of the definition above follows:
Given: - An information space, consisting of a set of information items - A visible set, consisting of the items in the information space visible to the user at a given time. This set will generally be a very small subset of all the available items in the space. - A set of choices, which depend on the current visible set. Each choice transforms the visible set to a new set of items. - Memory of previous views, choices, and consequences in the space - A fitness function, explained in more detail below
Produce: - A choice that improves the fitness function, as described below
This definition enables us to capture different kinds of navigation by expressing how a choice moves a navigator towards a goal. For example, search and exploration can be distinguished by their relevance functions and implied optimization criteria:
Search: Search is the process of finding items of a particular kind. Fitness is a mapping from a single information item to the set {O, 1} or to an ordinal similarity value. Choices should maximize the fitness of the fittest item in the visible set.
Exploration: Exploration is the process of building a mental model of an information space to facilitate inference. In exploration, fitness could be thought of as the difference between an expected view and an actual view. Choices should minimize this difference by directing the explorer to areas of the space where the mental model has the least predictive value.
18 Although this definition is a first approximation, its computational character brings several parts of the navigator's mental model into bright relief:
State: How will the navigator know where she is? Knowledge of the boundaries and extent of the structure will prepare navigators to make confident decisions. Lacking that knowledge, navigators can quickly become disoriented. For example, hypertext navigators can become confused after clicking on links that take them back to their current page, evidence that they don't understand where they are in relation to the choices they have [Spool97].
Choice: How will the navigator recognize the choices she has? Misunderstood or overlooked choices are frequent culprits in design investigations [Normn90]. For example, many buildings have doors that swing outward for fire safety yet have handles on the inside that suggest pulling the door to open it. Similarly, poorly emphasized image links in hypertext leave users wondering where to click or whether they have hit a dead end [WSTSk].
Inference: On what basis will the navigator make her choices? At each step, a navigator must make a choice based on partial knowledge of the space. Therefore, constructing an internal representation to facilitate inference is critical to getting around. In hypertext, users must infer a destination based on the label or icon attached to a link. The problems users have with poorly chosen labels and icons are well documented [InfAr98], [SunWb94]. Additional research suggests that finding unambiguous labels may be fundamentally very hard [Furns87]. Common design affordances to support inference include mouse-overs to punctuate available choices and the standardization of icons such as the e-commerce shopping cart.
Memory: How much does the navigator need to remember about the interface and her choices to navigate effectively? The need to ease a user's memory burden was recognized in even the earliest browsers; standard affordances include a stack of recently accessed items
19 traversable by back and forward buttons, a list of personal bookmarks, and special formatting of links that have already been visited.
The importance of state, choice, inference, and memory in navigation suggest specific criteria by which the navigability of a design may be measured. I propose that an information space is navigable to the extent that it enables users to accurately and easily answer the following questions:
Orient: Where am I? At any point during navigation, the user ought to be able to specify their current state in the information space.
Abstract: What things can Ifind here? Based on a brief exposure to the space, a user ought to be able to infer whether an item is likely to be contained in the space.
Wayfind: How do I getfrom here to there? The user ought to be able to generate an efficient path to a desired item in the space.
Predict: Where will this choice take me? The user ought to be able to accurately describe the items they might find if they were to follow a particular choice.
Remember: How will I do that next time? The user ought to be able to accurately and easily reproduce their navigation in the space.
I use these criteria to evaluate several information spaces throughout the thesis.
Digest of Previous Work
The Internet began in 1969 with ARPANet, a network originally designed to help academic communities share expensive computational resources. Tim Berners Lee devised the core technologies for the World Wide Web - the Hypertext Transfer Protocol (HTTP) and the Hypertext Markup Language (HTML). An excellent chronology of salient events up to 1999 can be found in [HOTIn99]. Up to date information on the Web's growth can be found at [HobIT].
20 Researchers are rallying around the need for usability. Norman has explored basic design principles for interfaces ranging from computers to door knobs [Norman90], has underscored the need to support the creation of an effective mental model of an artifact [Norman93], and has proposed reducing the complexity of information artifacts through the use of appliances, computational devices that support very specific activities and can share information between themselves [Norman98]. Nielsen has performed numerous software usability studies, has shown that 'discount usability studies' can be a fast and inexpensive way to locate and address usability concerns, and has distilled his experience down to a useful checklist for web designers [Niesn93].
Surprisingly, there appears to be neither a firm definition of the navigation problem nor a generally accepted list of criteria for its solution. Recent discussions have begun to untangle the various components of navigation [NavEW97]. Furnas has provided an important conceptual foundation by studying the formal complexity of navigation in directed graph structures and the effects of various navigation affordances [Furns97].
21 Chapter 2
Navigation in Hypertext
The end of our exploring will be to arrive where we started and know the place for the first time - T. S. Elliot
Overview
The invention of hypertext almost 30 years ago liberated information architects from the linear world of traditional print. Since that time, the growth of the Web quickly drew hypertext out of the research lab and into widespread use. The result has been a broad body of design experience in production environments. Recently, designers have begun to transform that raw experience into prescriptive principles and pitfalls to avoid.
This chapter reviews current practice in hypertext design from the vantage of a novice user. I identify a collection of design pathologies that recur in hypertext usability studies and state principles for their solution. I argue that these pathologies arise from a common cause: a mismatch between the structural organization of an information space and a user's perception of that organization as viewed through a page-centered browser. Beginning in Chapter 3, we examine an alternative to the page-based metaphor that promises to mend this perceptual breach.
Perceiving the Web
The Web is no longer the privileged domain of hardcore computer professionals. As inexperienced users continue connecting in large numbers, enhancing the experience of an untutored audience is becoming the challenge for web design.
How might an inexperienced user perceive Web navigation today?
Both the browsing interface and the design of the underlying hypertext shape any experience of the Web. After reviewing the general structure of the Web and the classical browsing interface through the eyes of a novice user, I examine a number of recurring hypertext design problems.
22 The Web Mosaic The Web can be thought of as a collection of sites, each containing a collection of information items. Although the technical notion of a site is defined by the way requests for information are addressed to servers, most users have, at best, a vague understanding of how the Web actually works behind the scenes. Instead, the perception of a site to an end user is largely determined by the conceptual relationships between information items and by the consistency of presentation style between pages.
Although individual sites may be coherently organized, our image of the Web as a whole resembles a vast, fragmented mosaic. One reason is that the Web is an enormous exercise in distributed design. There are millions of contributing authors, each with limited knowledge of related sites and widely varying views on how to situate their contribution in the greater whole. The mosaic continues to fragment rapidly: thousands of new sites and millions of pages are added each day.
The Web mosaic understandably intimidates many new users. Compare the experience of browsing the Web to that of visiting the local library. The lack of global structure across sites can make the Web seem like a huge pile of books: locally organized according to the conventions of the site designer, but missing the global structure that make a well-kept library relatively easy to browse. For example, a first-time user may be surprised to find that there is no obvious entrance to the Web. Furthermore, although a book has an obvious physical extent between two covers and a binding, its rarely clear how broad or deep any particular Web site really is.
How do users begin to get around in the Web mosaic? The unit of information access on the Web is the URL (uniform resource locator). A URL is a unique name used to refer to a particular item and a protocol for accessing it. URLs ground Web navigation in two ways. First, URL's provide an unambiguous way to refer to an item. Second, by separating the physical location of an item from its name, URL's permit the location of a resource to change transparently.
Although URLs address a critical problem, they do not in themselves provide a practical framework for navigation. There is barely a heuristic relationship between an item's content and its URL, and therefore no systematic way for a user to infer a document's URL based on its content or vice-versa.
23 PortalSites and Information Overload Portal sites are a response to the Web's fragmented image. By indexing the Web through keywords and hierarchical catalogs, portal sites offer users a natural front door to the Web. Unfortunately, the sheer scale of the Web makes precision a serious issue for any portal site. Keyword based engines routinely mire users in thousands of irrelevant hits. Categorically organized sites may not partition the world in ways that are meaningful to a particular user's task and may have leaf nodes that expand into sets containing thousands of items (e.g. [Yahoo]).
The Nearsighted ClassicalBrowser The first widely used graphical browser was Mosaic, which was freely distributed in 1993 [HOTIn99]. The creators of Mosaic left the National Center for Supercomputing Applications in 1995 to found Netscape. Since then, Netscape and Microsoft have dueled for dominance in the browser market. Remarkably, although virtually every aspect of the Web has changed dramatically in the years since Mosaic first appeared, the browsing interface has remained virtually unchanged. This is even more surprising considering that Netscape has opened the source of its browser [Netsc] and Internet Explorer freely exports virtually all its functionality to application developers as recyclable components [IntEx]. Considering the widespread use of the Web, one would expect freely available, production quality code to have stimulated improvements in browser design.
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The classical browser interface typically contains an address field at the top of the window in which users can directly type a URL. Back and forward buttons relieve the burden of remembering your path through a site by providing a stack of recently accessed pages. Users follow page hyperlinks by clicking on them; the target URL is often displayed in the lower corner. Finally, a folder of favorite links enables users to navigate quickly to items of interest.
The classical browsing interface is based on a page-centered metaphor drawn from experience with more familiar print media. When applied to the Web, the near-sighted view of the classical browser gives rise to an variety of interesting design problems.
Hypertext Navigation Pathologies
Hypertext usability studies have discovered recurring navigation problems. Although the symptoms appear superficially different, I will argue that many of these problems derive from a common cause: the page-based metaphor of web navigation fails to help users to construct a
25 mental model that extends beyond the margins of their current page view. The consequence is a mismatch between the organization of a hypertext and a users perception of it.
Lost in Hyperspace Hypertext frees designers from the linear organization of conventional text. One interesting consequence of this newfound freedom is that end users can have a difficult time knowing just where they are. In a seminal study, researchers found that navigators frequently reported feeling lost in densely connected hypertexts [Edwds93]. Studies of information foraging patterns reveal that many users navigate complex sites by fixating on a familiar anchor page such as the home page [Cantr85], [Spool97]. These users reorient themselves by returning periodically to their anchor page using the back button as a kind of tether. When searching for information, these subjects can be so eager to return to their anchor page at the outset of a search that they bypass the page containing their answer along the way without noticing [Spool97]. The perception of an anchor-based navigator is illustrated in Figure 3.
Although the ability to organize and access the same underlying information in multiple ways is a significant benefit of hypertext, sites that provide multiple access methods appear to aggravate the disorientation problem. For example, users who navigate a site primarily by its hierarchical organization can become lost when they perform keyword searches: upon following a search result link, users can become disoriented because they are not be able to situate themselves within their familiar hierarchy [Hardmn89].
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The lost in hyperspace distortion suggests a prescriptive design principle for navigation:
The Anchor Principle - Enable users to orient easily to a small set of salient locations.
As defined in Chapter 1, a navigable information space ought to help users to specify their current location and to reproduce their navigations. Anchors help a user specify where they are by establishing a primitive coordinate system: a user may specify their location relative to an anchor page. Furthermore, anchors enable a disoriented user to reorient by returning to a known location. In hypertext, anchors support the ability to reproduce navigations by reducing the memory load required to revisit items; encoding the location of an item in terms of a single route from a known anchor page requires fewer bits than recording its location in terms of an arbitrary route from an arbitrary page.
Contemporary hypertext designs often implement the anchor principle using a navigation bar (see Figure 4). Navigation bars provide a fixed set of shortcut links on every page in the site, thereby enabling users to return to pre-specified anchor pages in a single step. Note however that although navigation bars are a useful affordance for treating disorientation, they do not prevent it.
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Figure 4 - Tabbed navigation bar from Amazon.com
Silent Exits Different hypertexts rarely share the same organization, in part because different people construct them. As a result, leaving a site can be an important conceptual transition for a navigator: familiar anchors and choices may suddenly disappear and new orienting points must be found. Inexperienced users don't always realize when they've left a site [Spool97]. These users can wander several steps before realizing that something has changed, and become confused when unable to say exactly where the change occurred. Furthermore, inter-site links may terminate deep within the target site rather than at its home page, thereby leaving users without a clear sense of what their new orienting points ought to be. The perception of a user passing through a silent exit is illustrated in Figure 5.
Figure 5 - The reality (top) is a path that exits one organization and enters another. The perception (bottom) is a single undifferentiated path.
The transition principle is a prescription for avoiding silent exits:
The Transition Principle: Make organizational transitions explicit.
The transition principle enhances navigability by warning navigators to re-ask the important questions defined in Chapter 1 (i.e. where am I, what can I find here, etc).
28 Classical hypertext browsers distinguish hyperlinks in a page by underlining and coloring the anchoring text of a link. However, most sites do not distinguish links to destinations within a site from links that span different sites.
Leaps of Faith Users often have a difficult time guessing where a link will take them [Spool97]. Because it is generally very difficult to guess the content of a page from its URL, users must rely on the anchoring text of a link and its context within a page to infer its destination. Yet it can be very difficult to find concise labels that accurately describe a target page or site sub-graph; Furnas has illuminated the complexity of naming by observing that different people use a wide variety of terms to refer even to simple items [Furns87]. Studies of icon intuitiveness have produced similar conclusions [NieSo94]. As a result, poorly labeled links are widespread and searching a site can be frustratingly inefficient.
Icon Intended Meaning Perceived Meaning
Geographic view of a World, global view, planet, the companies branch offices world, Earth
Health field, money, health, care is expensive, Clinton's Benefits health plan, hospital, don't know, benefits
Public relations TV set, video, TV
System oriented, disk, CD, Product catalog computer, CD Rom
Briefcase, personal info, Specialized tools (toolbox) toolbox
What's new (bulletin board) Bulletin board, laundry
Figure 6 - Table comparing the intended and perceived meanings of hyperlink icons [NieSo94
One principle for managing the complexity of choices is the incremental commitment principle:
29 The Incremental Commitment Principle - Give users more than one level of detail to examine before deciding whether or not to pursue a given option.
One way to implement the incremental commitment principle is to supplement link labels with a small list of exemplary items that would be found upon traversing the link (see Figure 7). Another would be to use mouse-overs to present an extended summary of a link's destination; the duration of the mouse-over could be used to provide descriptions of different length.
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The incremental commitment principle improves navigability by helping navigators determine where a choice will take them and how to wayfmd to a particular item.
30 Hypertext designers are devising other techniques for avoiding leaps of faith. Designers are responding to the need for better labels by following common conventions. Virtually every large production site uses a navigation bar with a 'home' link on it, and many e-commerce sites use the shopping cart icon to represent a users current basket of purchases. Architecting a site with typed links representing consistent semantic relations between pages can also help users build accurate expectations.
Invisible Choices Modem web pages seamlessly blend rich media such as images and flash animations with text, giving designers the option to anchor hyperlinks to non-textual page elements. As a result, it is not always obvious to a user what their available choices are [WSTSk98], [Spool97]. When experienced users suspect they have hit a dead end, they may resort to scanning a page with the mouse to detect hidden hyperlinks in image content. However, unless care is taken in the presentation of the choices, inexperienced users may not even realize that they can click on images or animations at all. Figure 8 illustrates a page with invisible links.
Figure 8 - An early version of Saturn's home page. Can you guess which regions of the page are links and where these links might lead?
The concept of a 'virtual horizon' ensures that a navigator has at least one salient choice on every page:
31 The Horizon Principle - Give navigators a salient destination to navigate towards.
One implementation of the horizon principle is the use of a tour through the site. The navigator has the option of continuing on the tour by selecting a standard item in a consistent location at any page in the site. An example is illustrated in Figure 9.
Figure 9 - A virtual tour of the physics of the sun
By giving the navigator at least one salient choice on every page, a horizon encourages exploration and avoids dead-ends.
Other methods for emphasizing available choices are appearing in practice. Standard icons such as buttons and tabs offer visually suggestive choices and are familiar to most users. In addition, the use of dynamic graphics on mouse-over events can reduce the blind scanning of a page for active regions.
32 Page Islands There is often no visible indication on a page to help a user determine where they are relative to other pages in the site. On symptom of this problem is that users will often click on links that take them to the page they are already on [Spool97]. Similarly, hyperlinks that take users to an embedded location within their current page can lead users to believe they have actually jumped to another page. The perception of a user traversing embedded and reversing page links is illustrated in Figure 10.
Figure 10 - The reality (top) is a navigation sequence that follows links within a page and back to a previous page. The perception (bottom) is of distinct pages.
The Visible State Principle - Provide visible feedback on the user's current state relative to where they have been and where they are going.
The visible state principle improves navigability by helping navigators answer the question 'where am I?' Hierarchical sites such as Yahoo implement this principle by showing the path from the root of the hierarchy to the current page. Other sites use background colors or motifs to group pages that are conceptually related. To prevent users from following links to their current page, Nielsen and others have advocated simply shading them out.
33 Diagnosing Hypertext Navigation
Chapter 1 proposed several criteria for evaluating the navigability of an information space. These criteria provide a useful vantage for summarizing the design issues discussed in this chapter. To review, an information space is navigable to the extent that it enables users to answer several questions, including:
- Where am I? - What things can I find here? - How do I get from here to there? - Where will this choice take me? - How will I do that next time?
Page-based navigation makes it difficult for navigators to answer many of these questions. The classical browsing interface is nearsighted, focusing on single page views that disappear then re- appear without explicit cues to help navigators understand the relationship between pages. As a result, page navigators often fail to build an accurate model of the hypertext topology (i.e. 'Lost in Hyperspace'), fail to notice important transitions in the structure (i.e. Silent Exits), fail to guess where a link will take them (i.e. Leaps of faith), fail to notice meaningful choices (i.e. Invisible Choices) and fail to understand where they are (i.e. Page Islands). Clearly, principled page and site design can reduce many of these problems. However, the frequent mismatch between user perception and physical structure raise an important question: are there better alternatives to the page metaphor?
Ironically, most large sites have a 'site map' link on their navigation bar. Surprisingly, this 'site map' very often turns out to not be a map at all, but rather an exhaustive collection of links on the site more akin to an index (see Figure 11). In the following chapter, I examine the use of an explicit spatial metaphor in support of navigation.
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Digest of Previous Work
In 1945, Vannevar Bush envisioned a future where information could be stored on vast microfiches and accessed automatically by machines [Vbush45]. Twenty years later, Ted Nelson invented the notion of hypertext as a means to break out of the sequential model of information access in print. Two years later, Andries Van Dam had developed the first operational hypertext system at Brown and delivered it to NASA for use in the Apollo space program. By 1991, Tim Berners Lee had adopted hypertext for the World Wide Web and completed his work on the
35 seminal mini-Web at CERN. Within four years, use of the original Web server at CERN was growing by an order of magnitude each year.
Usability studies in hypertext have focused the need for better design. Modeska found that the navigational structure strongly affects perceived size: a large, strongly hierarchical site appears smaller than a small, flat site [ModMa97]. Hardman uncovered several navigational issues while observing users performing tasks on the Glasgow on-line hypertext [Harmn89].
In recent years, Information Architecture has emerged as a recognized design discipline and efforts are being been made to defme best practices. Flemming provides a broad review of current practice in hypertext navigation [Flemng98]. Flanders and Willis have collected several instructive case studies in poor design [WSTSk98]. Rosenfeld offers insights into the process of designing effective Web sites [Rosen98].
36 Chapter 3
The Spatial Metaphor
Interestingly, according to modern astronomers, space is finite. This is a very comforting thought - particularly for people who cannot remember where they left things. - Woody Allen
Introduction
Usability problems in pure hypertext invite alternatives to the classical page metaphor. This thesis is guided by the idea that a spatial metaphor can significantly improve Web navigability. The spatial metaphor itself is not a new idea; the notion of mapping information to objects in a virtual space is older than the Web itself [VernV8 1], [Gibsn84]. However, while two-decades of development have produced dozens of mock-up spaces and concept browsers, there has been little progress towards a principled design framework grounded in formal usability studies.
This chapter examines the logical foundations of the cyberspace5 metaphor and outlines the goals of this thesis. I propose that the Aperture Problem is a key link through which insights from physical spaces may be transferred to the Web. With respect to the criteria for navigability outlined in the previous chapter, I hypothesize several ways in which a spatial metaphor could enhance Web navigability. I identify a collection of representational elements drawn from environmental psychology as the core of a design framework. Lastly, I frame the pedagogical and applied goals of this thesis.
What is The Spatial Metaphor?
Metaphors are a common technique in interface design. By leveraging experience with familiar items, metaphors can help users to create working mental models of novel artifacts. Common examples in computing include files and folders for organizing persistent storage, the recycle bin for deleting objects, a window as view into a program's operations, and a desktop as a working
5 I will use the term 'cyberspace' to denote an information space designed with a spatial metaphor.
37 area. Proposed metaphors for organizing the Web have included books, libraries, and various types of viewing lenses [InfoVz99].
The spatial metaphor is an interface design in which information items are mapped to objects in a virtual space and navigation corresponds to movement of the user's viewpoint relative to objects in the world. For example, Narcissus [Narcs95], an early virtual reality browser, mapped Web pages to spheres in 3-space and hyperlinks to cylinders joining the sphere centers. An example of this presentation is illustrated in Figure 12. Worlds like Narcissus have gained popularity in recent years due to the availability of language standards such as VRML (virtual reality modeling language) and improved development tools [VRMLo].
Figure 12 - A very simple VRML world
Users may navigate in VRML worlds in several ways: translation and rotation in either object or view-centered coordinates, or by smoothly animating to a selected item. The most popular VRML browser and several demonstration worlds can be freely downloaded at [Cosmo].
Immersive 3D environments are only one implementation of the spatial metaphor. Other popular choices include a 2D canvas and a 2.5D view in which the user navigates along a plane in 3D as they would in a city. Although the choice of presentation style is obviously a very important and
38 offers interesting avenues for research, this thesis will focus instead on the usability implications of associating information with locations in a virtual space.
Inside the Spatial Metaphor
Although provocative, it is by no means obvious that a spatial metaphor is an effective approach to navigating information spaces. For example, unlike physical space, virtual environments are not constrained by laws of physics such as impermeability, conservation, and continuity. Why might we believe that our expertise navigating in physical worlds can be profitably transferred to the Web? Why choose this metaphor rather than some other approach such as the page metaphor? What are the usability consequences of this metaphor? Previous work has not adequately addressed these questions.
This thesis claims that navigation in physical space and navigation in information space are closely connected because navigators in both spaces must solve the same fundamental problem:
The Aperture Problem - Given a world where the available information is too large to be seen in a single view, and given choices that move the current view to new areas of the space, construct a mental model extending beyond the immediate view that enables effective choices to be made.
Both physical spaces such as a city and information spaces such as the Web are far too large to be seen completely in a single view. Classical browsers sidestep this problem by presenting single- page views and enabling users to jump discretely between pages by following hyperlinks. As the usability survey in Chapter 2 illustrates, a collage of disjoint, single-page views can make it very difficult to build a mental model that extends beyond the margins of the current page. From the vantage of the Aperture Problem, navigating the Web using a classical browser is like trying to find your way through a city in dense fog.
39 Figure 13 - The Aperture Problem: How Do Navigators Build a Model of a Large World from Local Views?
My focus on the Aperture Problem distinguishes this effort from previous research in Information Visualization. Prevailing trends in visualization argue for physical space as a powerful metaphor because the information bandwidth to our eyes is very high. This line of research has produced several clever techniques for increasing the amount of information that can be made available in a single view. For example, fish-eye browsers use an explicit focus of attention to represent items near the center of the viewpoint at higher resolution [Fishey8 1] [Inxht]. Non-Euclidean geometry [HypVz95] and extensions to three-dimensions [Munzr97] can be used to further increase the information density. Johnson and Schneiderman invented tree maps as a way to visualize hierarchies while making optimal use of the available display area [JonSc9 1]. By focusing on the Aperture Problem, I will assume from the outset that there is too much information to be seen in a single view, no matter how clever the presentation technique.
40 Figure 14 - View of the Barnes and Noble on-line bookstore via the Inxight Hyperbolic Lens Visualizer [Inxight]
In the previous chapter, I defined knowledge navigation as the process of accessing information by selecting choices. This definition illuminates several reasons why the spatial metaphor might enhance navigability:
We are All Experienced SpatialNavigators: We navigate in a spatial world every day. In particular, spatial operators like left, right, up, down, in, and out are familiar to users and need no explanation. Furthermore, these choices can be made available in every view, thereby making it more likely that users will recognize the choices they have.
41 Where You Are and How You Got There are Not the Same Thing: Because user memory is a precious resource, navigable spaces ought to minimize the amount of information a user must remember in order to navigate. Navigation in hypertext is procedurally based: the user returns to a page typically by following a known sequence of hyperlinks. Navigation in physical space could reduce memory demands by enabling users to see where they are rather than remembering how they arrived there. In addition, because navigators in physical spaces can move freely in each dimension, users can navigate more efficiently by generating novel paths.
No Page is an Island: Because choices made while navigating are based on inference to the location of useful items, users need both a model of their current state and information about where choices might lead. Hypertext provides minimal contextual information to support user inference beyond the current page (e.g. link labels and icons). A spatial metaphor could help support inference by, for example, transforming hyperlinks into arrows pointing in the direction of the link destination. If the space is designed to impart meaning to directions, arrows from hyperlinks could help users navigate more accurately by enabling them to draw on their knowledge of items they have seen in that direction.
This thesis will focus on manual design informed by the cognitive properties of navigable cyberspaces. Emphasis on design policy distinguishes this effort from tool-driven approaches. Generating automatic layouts of virtual spaces from directed graphs has been a recurring theme in information visualization research [IngBn95], [Narcs95], [Munzr97]. Although clearly important for scalability, previous efforts in automated layout do not address a crucial prior question: what properties should such layouts have in order to support the cognitive requirements of the end user? Studying how users build mental models of relatively small, handcrafted environments can greatly enhance the focus of future work on automated approaches.
LRPDP: A Collection of Spatial Design Elements
Research in cognitive science has produced insights into the models people use to navigate in complex physical environments. Lynch's seminal work examined the way people navigate in cities [Lynch60]. He discovered that people appear to use a relatively small set of representational primitives to navigate in large environments:
42 Landmarks are distinguished features of the environment that help people orient themselves and calibrate distance. Landmarks are one of the first things people acquire in a new environment. In a city such as Boston, landmarks are often tall buildings such as the Prudential Center, while in rural areas they may be geographic features such as a volcano or a body of water.
Regions are abstractions that people use to identify bounded regions of the environment. Neighborhoods can be grouped based on geographic, cultural, economic, or personal characteristics (e.g. respectively, the waterfront district, the Italian quarter, Park Avenue, and the place I grew up). Related to the notion of region is the notion of boundary: a physical edge representing a transition from one region and another.
Paths are recipes people use to get from here to there. In most environments, our ability to navigate appears to be based largely on path knowledge [Chase8 1]. For example, it is not uncommon for people to live in a large city for years without realizing that two familiar places, visited using completely different routes, are in fact right next to each other.
Directionskeep people oriented by giving them a canonical coordinate system in the environment. Directions can be based on global features, such as the direction of the setting sun, or local features such as the direction to the lake or Time Square.
Proximity enables people to recall the location of a place in terms of the places it is near.
Some of Lynch's original elements have been omitted from this list because they imply physical constraints that need not exist in cyberspace. For example, edges are boundaries of the environment that are not traversable on foot, such as an expressway or a waterfront. In cyberspace, the restriction on movement implied by edges is unnecessary.
The LRPDP elements implement several of the design principles discussed in Chapter 2:
0 Landmarks implement the anchor principle by providing salient locations
43 * Regions implement the transition principle by placing explicit physical boundaries around conceptually related items. " Paths implement the horizon principle by providing a prescribed trajectory through the space. * Directions avoid leaps of faith by enabling interpolation and extrapolation * Proximity avoids leaps of faith by facilitating prediction through nearest neighbors
The concepts of landmark, region, path, direction, and proximity form a promising foundation for spatial design that will be explored in the remainder of this thesis. In the following chapter, I will illustrate how LRPDP design can be applied to the Web by presenting a portfolio of sample cyberspaces.
Previous Work The heritage of cyberspace began with Vernor Vinge's novella 'True Names' [VernV81], but the term cyberspace is credited to Gibson [Gibsn84].
Linguists and philosophers have argued for the primacy of metaphor as a foundation for understanding. Lakoff has explored the role of metaphors in language and problem solving [Lakof8O]. Johnson has argued that abstract representations of the world may be predicated upon basic physical interaction with the world [Jonsn87]. These investigations highlight spatial representation as a fundamental substrate for abstract reasoning.
Several hypertext studies have implied the need for a spatial representation of the Web. Parunak articulates several navigational strategies employed in the physical world and how they may be applied to hypertext [Paruk89]. Hammond and Allinson found that the use of a travel metaphor as a design principle helped users learn how to navigate an educational hypertext [HamA187]. Edwards and Hardman present evidence that hypertext navigators may try to build a cognitive survey map while navigating [Edwds93]. Although previous work has identified the need, it has not evaluated the impact of the metaphor.
There have been many concept browsers and mock-up spaces produced since the Web's inception [InfVz99]. Andrews [Andrs95] and Hendley [Narcs95] explored mapping hypertext structure into 3D cyberspaces using force directed placement. Johnson and Schneiderman invented tree maps as a way to lay out hierarchies while making optimal use of the available display area [JonSc91].
44 Rennison and his group at the Media Lab have developed the spatial metaphor through a virtual news galaxy [Rensn94]. Card, Mackinlay, and Roberston have produced many visualizers in their research at Xerox Parc, including 3D rooms [RbMaC93], the Web Book [CaRbY96], the perspective wall [MaRbC91], cone trees [RbMaC91], and the Inxight commercial web browser [Inxht]. Small has illustrated how immersive environments can be used to represent textual information by designing a virtual world containing all of Shakespeare's works [Smal196]. As a complementary approach to these advanced presentation methods, I will center my attention on the navigator's perception of an information space through a mental model.
Tufte's panoramic collection illustrating the spatial presentation of information is considered to be a landmark in the design community [Tufte89, Tufte90, Tufte97]. In particular, Tufte's emphasis on prescriptive principles provides a precedent for this research.
Lynch's early work established the power of landmarks, regions, paths, and directions as design concepts for coping with the aperture problem [Lynch60]. Ingram sought to extract these features automatically through syntactic analysis of large directed graphs [IngBn95]. My emphasis here is on knowledge-based design principles process rather than automated syntactic methods.
45 Chapter 4
Case-Studies in Information Architecture
Few things are harder to put up with than the annoyance of a good example. - Mark Twain
Introduction
Design precedents teach us that a body of experience is necessary before the outlines of a theory can be seen with confidence. In the previous chapter, I argued that a spatial metaphor can be useful for navigation and proposed that primitives such as landmark, region, path, direction, and proximity (LRPDP) can serve as a design framework. In this chapter, I characterize the aspects of an information space that make it appropriate for a spatial metaphor. Conversely, I argue that certain kinds of spaces do not benefit much from a spatial approach. I illustrate my views by applying the spatial metaphor to a portfolio of four sample information spaces. Each space demonstrates how a broad class of user activity can be viewed as a navigation problem and how the LRPDP elements can be applied in its solution.
A Simple 2D Overhead Presentation Technique
I will use a 2D overhead presentation technique throughout this thesis. In this presentation style, items of information are mapped to areas in a plane. The viewing plane and the mapping plane remain parallel with their coordinate axes aligned; no rotation is allowed. The viewing plane may translate freely in the half-space in front of the mapping plane.
46 Figure 15- Schematic of the 2D overhead presentation technique
The overhead presentation is simple yet sufficient for exploring the questions of interest to this thesis. First, two-dimensional visualizations enable higher information densities than many three- dimensional techniques because the restricted viewing angle enables most of the display area in every view to be mapped with information items; in three-dimensions, many views may be highly occluded. Second, two-dimensional visualizations typically permit much faster interaction than three-dimensional worlds because users have difficulty navigating in three degrees of freedom6 and the most familiar input device (i.e. the mouse) is two-dimensional. Lastly, eliminating rotation removes the need to track the relative orientation, thereby reducing the user's memory burden. Devising advanced methods for visualizing large collections of information is a rich topic in information architecture [InfVz99]. However, this thesis seeks instead to understand how associating an item of information to a location in space can enhance navigability through the creation of a mental model.
When Is Space Useful?
As defined in Chapter 1, an information space is an organized collection of data supporting a human activity. Implicit in this definition is the principle that the organization of an information space should not be separated from the activity it is designed to support. Therefore, recognizing
6 See, for example, 'Why 2D is Better than 3D' at http://www.useit.com/alertbox/981115.html.
47 when a spatial metaphor is appropriate requires understanding when and how the metaphor will support a particular kind of activity. The following attributes illustrate how the structure of an activity can affect the relevance of the spatial metaphor:
Multi-Representational Tasks that involve several distinct sub-tasks can require different methods of access at different times. For example, searching for specific names suggests keyword search, searching for job categories suggests browsing a hierarchical view, and learning about a subject suggests traversing a path of pre-requisites. Tasks that shift between access methods can be disorienting in hypertext. Upon following a link returned from a keyword search, how will the user know where they are within an overlaid hierarchy or tour path? Once again, the problem is that hypertext does not readily separate where you are (e.g. at a crossroads page detailing related sites of interest) from how you arrived there (e.g. by keyword search, by specializing a topic category, by navigating to the end of the main path). By separating where the user is from how the user got there, a spatial metaphor can help keep users oriented as they shift between these access methods. Examples of multi-access information activities include planning a vacation or a wedding. Negative examples include one-shot tasks such as retrieving a particular income tax form from the IRS web site.
The Multiple Access Test - If there are many ways to get from here to there, consider a spatial metaphor.
Contextual For some activities, relational structure between items can be as important as the content of the individual data items themselves. A spatial view can significantly enhance a user's ability to grasp non-local properties of an information space, particularly in organizations with richly typed links. The importance of visual context is emphasized throughout visualization research [InfVz99]. Examples of contextual spaces include spaces that model causes and effects, such as tracking critical path dependencies in project management. Negative examples include spaces with relatively sparse, flat relational structure with weakly typed links, such as un-moderated news groups or classified ads.
The Contextual Test - If decisions depend on more than two items at a time, consider a spatial metaphor.
48 Revisited A user must learn the locations of salient visual items and their conceptual correspondences in order for the spatial metaphor to be useful. As such, a spatially organized information space is most effective when the cost of learning can be amortized across frequent visits. Conversely, if the user is simply searching for a well-defined item with no intention of returning to the space, there is relatively less value in supporting extended navigation with a spatial metaphor; a simple hierarchical approach implemented in plain hypertext may be equally effective. Examples of frequently revisited spaces include verifying a diagnosis in the physicians desk reference, organizing your work within a file system, and planning your meals within a virtual cookbook. Negative examples include one-shot activities such as on-line registration of a software purchase.
The Habitat Test - If the supported activity occurs infrequently, a spatial metaphor may not be worthwhile.
The development of a taxonomic system of classification for information spaces is an important long-term goal for information architecture. The tests above form a modest beginning for this larger effort and the role of a spatial metaphor within it. Additional attributes to consider could include dynamic (is the data in the space accumulative only? how fast does the data and its organization in the space change?), communal (who else is in the space? what are they currently doing?), and co-constructed (where should put my contribution to the space? how does my contribution relate to existing items?).
I will now present a series of examples illustrating how the spatial metaphor can be applied to several classes of user activity. For each example, I outline the class of activities being examined, specify the available data used to construct the space, motivate the architecture used in the design, and discuss observations and lessons learned. The first example demonstrates how expert domain knowledge embedded in LRPDP elements can be used to elevate citation spaces into intellectual histories.
Exploring the Evolution of Ideas in the MIT Vision Space
Activity New researchers often struggle to find references to seminal work and to understand the lines of inquiry that produced them. Large citation databases have been made available on the Web in recent years [WbSci], [CitSr]. Unfortunately, because the interfaces to these databases are almost
49 exclusively keyword driven, it is difficult to get answers to important questions a new researcher is likely to have:
What were the defining points in the development of thisfield? What are the key concepts that structure and differentiate ongoing work? Where are the most promising areastofocus?
Citation spaces pass the multiplicity test because chronology, author name, and subject are all commonly used access points. The relational test is passed because the ancestry of a piece of work is typically very important to understanding its contribution. The habitat test is passed because researchers must stay informed of ongoing work.
Data The MIT Al Vision Space contains abstracts of technical reports and memos collected over 30 years of vision research at the MIT Artificial Intelligence Laboratory. A small subset of these reports were accessible on-line via a free-text keyword interface or by browsing in chronological order; the remaining original reports were available only in hardcopy.
I identified a total of 500 abstracts related to machine vision research dating from 1960 to 1995 and converted them into a standard hypertext format containing the title, authors, date, and abstract body.
Architecture Understanding how vision researchers think about vision was the first step in the design process. Interviews with two professors at the lab provided insights into the conceptual structure of vision research. These concepts and their representation in the space are listed in the table below.
Concept Desien Element Seminal Paper or Survey Landmark Problem and Sub-Problem Region Cause and Effect Path Low-level to High-level Vision Direction
Figure 16 - A physical metaphor for the MIT Al Vision Space
50 Important papers and surveys provide orienting points. These papers are represented as highlighted landmarks. Papers are grouped into topics such as motion, stereo, and surface reconstruction; these topics are represented as labeled regions in the space. Historical chains of cause and effect over time are represented as paths. These chains were largely reconstructed through conversations with domain experts. Finally, moving North through the space, the user progresses from low-level vision topics such as retinal processing to high-level vision topics such as object recognition. A snapshot of the area of the space covering work on motion is shown below.
Figure 17 - Snapshot of the MIT Al Vision Space
Observations The Vision Space is an excellent illustration of the Knowledge Principle [LenFg9 1] applied to knowledge navigation:
The Knowledge Navigation Principle -
51 The navigability of an information space derives from the specific domain knowledge embedded within its organization
According to this principle, information architects ought to capture domain specific knowledge and communicate that knowledge to the user. In the Vision Space, the explicit use of notions such as low to high-level vision, the factoring of problem areas, and the selection of landmark papers reflect knowledge captured from domain experts. The LRPDP elements are the vehicle for communicating this knowledge to the user.
A knowledge-based approach to information architecture is by no means the only approach. Several lines of work have focused on purely automated methods for organizing information spaces using syntactic properties of the underlying items [CKPTu92], [IngBn95]. These methods can be applied to very broad classes of information spaces (i.e. free-text, trees, directed graphs) and can be scaled to large collections. However, existing methods offer little assurance that the resulting organization of a particular space will make sense to the end-user. For example, although selecting nodes with high in-degree to be landmarks appears to be a sensible heuristic, nodes may have high in-degree for very different reasons (e.g. an important paper, an early paper, a paper by a prolific author). A user needs to know why an element has been represented a particular way. Without this knowledge, the user's ability to make reliable inferences is compromised. A knowledge-based approach encourages consistent, meaningful semantics throughout the space. Unfortunately, the high level of manual effort required to architect knowledge-based designs can severely limit their scalability.
Troubleshooting in the Microsoft Outlook Help Space
Activity Software is notoriously difficult to use. One source of this difficulty is the expansive range of potential states and operations available to the user. In addition, it is well known that users typically don't read instructions and may even decide whether or not to use a piece of software based simply on the size of the manual [Niesn93]. The chemistry of an impatient user and a feature-rich artifact make support one of the most expensive phases of software development.
As a habitat with multiple points of entry, on-line support appears well suited to a spatial metaphor. Consider also the correspondence between the questions new users struggle with and the questions navigators struggle with, as defined in Chapter 1:
52 Software Ouestion Navieation Ouestion What can I do with this program? What can I find in this space? How do I perform this action? How do I get from here to there? What will happen if I press this? Where will this choice take me? What is the program doing? Where am I? How did I just do that? How will I get there again?
This correspondence suggests that it is natural to view the process of interacting with software in general, and the support activity in particular, as a navigation task. To the extent that a spatial metaphor is effective in addressing the knowledge navigation problem, it may also have a positive impact on the software support activity.
Data Microsoft Outlook is a popular, multi-purpose program designed to help users manage email, scheduling, note taking, and contact information. The standard help facility is a hypertext-like design in a Microsoft proprietary format. I collected about 300 items from the help facility and converted them into standard hypertext.
Architecture The features of Outlook were factored into regions in the space. The internal structure of each feature region was in turn represented using the following design pattern:
* Introduction - a summary of the feature * Use Cases - instruction on performing common tasks. * Setup - instructions specific to enabling the feature * Customization - how to personalize aspects of the interface * Troubleshooting - answers to frequently asked questions and typical problems * Glossary - terms related to this feature
For each feature, this design pattern was mapped to the spatial cliche shown below. This spatial clich6 was introduced to help users make predictable choices. For example, users at the introduction page of the calendar feature region could infer that moving up and to the left would take them to the glossary of terms related to scheduling.
53 LE-W -I
Gbssary Custc~miz~nCu stomized iDn
cJ)a,
f
Troubleshooting Setup
Introduction
Figure 18 - The spatial design pattern of an Outlook feature
A guided tour through the space was provided. Each tour stop smoothly animated the user's view to a location in the space and a played a short audio clip describing an aspect of the design. The tour stops, with a transcription of each clip that was played, are provided below:
1. Welcome - Welcome to Microsoft Outlook! Outlook is a program designed to help you organize your email, calendar, notes, and contact information. This short tour will show you what Outlook can do and where you can find answers to your questions. 2. Features - The features of Outlook are represented as colored regions in the space. You may click on a region to zoom in and center on it. Please select the email region to continue. 3. Pattern - Each region in the space is organized using a common pattern. The red landmark at the bottom represents the home page for the feature, where you can find general information about the purpose and scope of the feature.
54 OWN - M
4. Setup - The lower-right area of each region contains information on how to setup the feature. This item describes how to setup an email service, an essential first step to getting started with email. 5. Use Cases - The middle area of each region contains instructions on how to use the feature. You can follow a path to learn about additional operations: this path shows you how to author and send a piece of email. Please follow the path to the end to continue. 6. Customization - The upper-right area of each region describes how to customize the feature. This item describes how to automatically add a signature to your outgoing email. 7. Troubleshooting - The lower-left area of each region contains troubleshooting information and frequently asked questions. This item discusses what might be wrong if you are unable to send mail. 8. Glossary - The upper-left area of each region contains a glossary of terms related to the feature. The terms are laid out in a alphabetical order along a single, zigzagging path. This item defines what SMTP stands for.
What is Inbox?
. Search for Information: Search for information the same way as you would on the Web. Just enter the text you are looking for and click Find Now, or click Advanced Find to pinpoint your search. . Manage your Inbox: Click Organize to use Outlook's powerful tools for manage your e-mail messages.For example, create a rule that moves all of the messages from your Inbox into separate folders.Or intercept messages that are suspected ofbeing junk e-mail and have them moved to a folder or deleted.With AutoPreview, you can preview the first few lines of text in all of your messages or only in the messages you haven't read. . Flag for Followup: When you want others to really take note of your message, use Flag for Follow Up to get their attention. The ag appears in their message list, and the action you want them to take note of appears at the top of the message You can also ag messages for yourself, and fag contacts. " Color Messages: You can create rules to color-code messages that meet criteria you specify. For example, you can set up a rule so that all messages you receive from your boss appear in blue text, making it easy for you to identify important messages. " Format Message Content You can use a vanety of fonts, font sizes, font styles, and colors in the text of an e-mail message. You can also change the way text is aligned and indented or use an automatic format to quickly create a bulleted listUse a siature to automatically add text to messages you send. For example, create a signature that includes your name, job title, and phone numberIf you need additional formatting features, such as tables or text hilglighting, you can use Microsoft Word as your e-mail editor.
Figure 19 - Snapshot of the Outlook Help Space at the third tour stop
55 Observations An important principle gleaned from the design of the Outlook space was the Situated Action Principle:
The Situated Action Principle - Teach users in the same place they use what they learn.
The tutorial space and the reference space ought to be the same space. This is typically not the case in most existing on-line support: users must access a separate resource to get help. Providing a tutorial in the same space can help users associate the elements of the tutorial with related areas that will be needed later for help.
Two additional techniques were used in the design of the Outlook Space:
The Spatial Clichi': Reinforce semantic patterns with spatial cliches. The consistent spatial organization of a semantic pattern can help users form expectations about the consequences of their actions. These expectations are the especially critical for navigation when only part of the space is visible in any view.
The Guided Tour: A guided tour is a useful technique for introducing a navigator to the organization of an information space. Several principles were used in the design of the Outlook tour:
The Active Learner Principle - Ask the navigator to perform tasks in the process of learning the structure of the space.
Lessons in perceptual research suggest that people learn and retain more when they must act upon the information they perceive []. This suggests that a tour should include stops where users are asked to perform a small navigation task based on what they have learned.
The Exhibit Principle - Reinforce the abstractions of the space with specific, proximate examples.
56 The ambiguity of language makes it difficult to communicate concepts accurately; this is an especially difficult problem in interface design [Furns87]. As such, providing specific examples is essential to grounding the meaning of the LRPDP elements.
The Homing Principle - Revisit landmarks in the tour from multiple trajectories.
Landmarks serve as familiar orienting points for users. Follow a trajectory that enables a familiar landmark to be seen from multiple perspectives so that users can relate new items to ones that are more familiar to them.
The Footstep Principle - Distinguish items that have already been visited from novel items.
The distinction between visited and novel items is fundamentally useful because it enables a navigator to ignore certain items in the space: an exploring navigator may focus on novel nodes, while a navigator returning to a known page may focus on previously visited items.
One can imagine a much more fme-grained approach to a spatial metaphor for software support. Consider representing a pattern of software use as a trajectory in a virtual space. Any software component is describable as a finite state machine. By representing user-visible states as locations in a space and the operations between states as path elements, a pattern of usage becomes a trajectory in the space. Such a design would enable the user to track the state of the program and their interaction history at any time by determining the location and path of their current view. This ability to orient is particularly important in multi-step activities or at states offering very many choices. Interestingly, a similar representation of user activity already exists internally in Outlook: within the Office Paperclip Agent, a small window that makes suggestions and offers help during use. This agent uses a Bayes network of software states to determine when and how to provide help.
Certain areas of the outlook space contained items that were relatively unrelated; these areas illustrate cases where the spatial metaphor is not especially useful. For example, the customization area of the email region described how to change the format of messages, to hide
57 certain header fields, and to add a custom signature. The lack of strong relational structure among these items meant that the location of a particular item had no meaning beyond its containment in the customization region. In such cases, a conventional unordered list would be more a more space-efficient representation.
Learning About Dinosaurs in the Virtual Dinosaur Exhibit
Activity On-line learning spaces are an important class of information architectures offering the potential to provide high-quality educational materials to a very broad audience while offering students more control over when and how they learn. The design of on-line learning environments can benefit from experience with conventional educational designs. For example, a museum exhibit is a spatial environment designed to facilitate exploration and learning. Unlike a traditional course, museum exhibits enable a visitor to browse and interact in a free-form manner. In virtual exhibits, supporting effective exploration through navigation is an important goal. To what extent can principles from exhibit design be transferred to the design of on-line exhibits?
Data The Virtual Dinosaur Exhibit is a collection of about 100 facts about dinosaurs. These facts were culled from several popular sites on dinosaurs, including the BBC's Walking With Dinosaurs Site [BBCDn] and the Enchanted Learning Dinosaur Exhibit for kids [EnlDn].
Architecture The exhibit was designed around a narrative represented as a looping path through the space. Segments of the path proceeded through regions of the space that were mapped to topic areas. The progression of the narrative followed natural dependencies among the information items:
1. Introduction - Welcome to the Virtual Dinosaur Exhibit 2. Classification - What are dinosaurs? 3. Exhibit - Individual dinosaur profiles and the periods in which they lived 4. Extinction - How did the dinosaurs die out? 5. Fossils - How we collect and interpret evidence from the fossil record 6. Anatomy and Behavior - Facts and theories about how dinosaurs lived 7. News - Recent events in paleontology
58 Two design patterns were used in the space. Within the exhibit region, individual dinosaur profiles were organized according to the time period in which they lived and the part of the food chain they occupied. The periods were laid out chronologically from South to North. At the description of each period, an upward sloping branch was used to represent the progression up the food chain from the climate to plants, to herbivores, to carnivores. Within most of the remaining regions, smaller loops were used to offer more detail on topics that eventually merged back into the main narrative path.
Carnivoires of the Triassic eat-eaters of the Tnassic Period included
" Coeloohln - An small but adept killing machine . Postosuchus -Tri biggest predator of its imne " Cynodont- A mammal Ike reptle . Petenosaurus - An earty pterosaur
Figure 20 - Snapshot of the virtual dinosaur exhibit
Observations The virtual dinosaur exhibit is a path-based organization based on three principles:
The Main Street Principle - Provide a central orienting path through the space.
59 A central orienting path imposes an over-arching context on the flow of information and gives users the option to explore the exhibit in a prescribed manner. This is especially important when dependencies exist between items; if item A ought to be seen before item B, then the organization ought to encourage visitors to proceed to B through A.
The Visible Destination Principle - Tell navigators where a path will eventually take them.
The end of a path is a salient feature for users because it gives them something to move towards (e.g. it implements the Horizon Principle from Chapter 2). Without this sense, users may choose not to explore a path at all. This is one of the virtues of a spatial visualization: in many cases, the entire path can be seen at once.
The Measured Extent Principle - Tell navigators how long a path will last.
This principle is related to the previous one. Without a sense of how long a path will last, a user cannot judge whether or not it is worthwhile to traverse it. As with the previous principle, visualization of a path gives users immediate access to its extent.
Sense-Making in the Thinkubator
Activity Organizing your thoughts can be a difficult and time-consuming process. For example, in preparing this thesis, I reviewed a wide variety of primary materials representing ideas I had collected over years of work: several notebooks, web pages, audio tapes, phone messages, stickie notes, and comments in program source code. Distilling these materials into a single coherent document demanded many months of concentrated effort. In some cases, ideas were lost because I either couldn't read what I had written or had simply forgotten what I really meant.
Why is it so difficult to organize our brainstorming activity? I propose two basic reasons:
Ideas are Opportunistic: Many of our most important ideas occur at unscheduled hours and places: at a water cooler, listening to a talk, reading the newspaper. Rather than risk losing a good idea, we
60 often try to record our thoughts using whatever materials are immediately available. The result is a partial, barely decipherable, heterogeneous record of our experiences.
OrganizingIdeas is an Activity in Its Own Right: Organizing ideas is a very different activity from actually generating ideas. Finding common structure requires taking a step backwards, which can be very difficult given the narrow focus required to complete the immediate task at hand.
The brainstorming activity is much more complex than the activities I've explored in previously mentioned spaces. Where earlier spaces involved navigating a well-defined organization, brainstorming involves constructing an evolving organization over time. As such, brainstorming in the Thinkubator is not a pure navigation task. However, the spatial analogy of a blackboard suggests that a spatial metaphor may be a useful approach to organizing ideas. How might a digital blackboard extend and enhance the properties of its physical counterpart?
Data The Thinkubator is a digital blackboard I designed to help myself capture, consolidate, and communicate my ideas. The data items are notes that can be assigned positions on the blackboard. I have used the Thinkubator to prepare presentations, draft papers, summarize meetings, and consolidate ideas that collect over time. The spaces I have built range in size from about 20 to about 200 items.
Architecture Various types of notes populate the Thinkubator blackboard. Each note belongs to a single category in a taxonomy of ideas that I created, listed in the table below. Motivation notes describe points of departure for problem solving. Idea notes describe approaches to a problem and record observations. Action notes cover projects to undertake. Result notes summarize lessons and artifacts produced. Reference notes are pointers to papers and on-line resources.
* Motivation - Question - Problem " Idea - Observation
61 - Example
- Hypothesis * Action
- Experiment
- Program * Result - Principle - Claim - Artifact
This list represents a first step towards a taxonomy of ideas. Additional concepts such as analogy, counter-example, and exception would be useful additions, but the further development of this list is an engaging research topic in its own right.
Notes are collected into topic regions and linked into chains of cause and effect relationships. The design pattern for linking notes proceeds from Motivations, to Ideas, to Actions, to Results. This design pattern represents the achievement of an important brainstorming plateau (i.e. developing an idea from its motivation to its consequences) with a salient spatial artifact (i.e. the formation of a complete path). A snapshot of the Thinkubator interface is shown below.
62 KCL-
!Armies of people are studying keyword search, but almost no work is being done to improve the navigability of the Web.
Figure 21 - A snapshot of the Thinkubator interface
Observations My ongoing experience with the Thinkubator has identified interesting phases in the development of the ideas on the blackboard over time:
1. Generate: In the first phase of development, I freely generated and added thoughts to the blackboard. The brainstorming principle I attempted to follow was to suspend evaluation or questions of how to organize the ideas, focusing instead on simply generating as many different alternatives as possible. At this stage, the positions of the items have no intentional semantics.
63 0 0
* 6 S S * S
Figure 22 - The generation stage. Ideas are added opportunistically.
2. Group: In the next phase, ideas on the board are grouped into piles of related notes, forming a contextual area. The key brainstorming principle is to divide and conquer. The supporting spatial principles are the use of explicit boundaries to separate regions of the space and the placement of related notes in proximity to each other. Categories on the blackboard were non-overlaping: when a note appeared to belong to more than one category, I replicated a reference at another location.
S S S
Og
S S
Figure 23 - The grouping phase. Notes are collected into groups of related items.
3. Make Connections Explicit:
64 ...... I,-
In this phase, connections between individual notes are represented explicitly. The key brainstorming principle is to make relationships explicit. The supporting spatial principle is to enable users several ways to navigate freely in the canvas (e.g. a multi-scale view).
Because of the limited ways to represent proximity relationships in a planar view, there are typically many related notes that appear in physically separated areas of the canvas; these are important to locate and bookmark in this phase since they would be likely to be overlooked later in the spatial view. I sidestepped this planar view problem by replicating notes at more than one location.
Figure 24 - The linking phase. Local connections between individual notes are added.
4. Identify a Primary Path: In this phase, the ideas on the board are funneled down into a primary causal chain containing at least one motivation, idea, and action. I used this path to place the remaining ideas on the blackboard in context as either supporting aspects of the path or tangents for later investigation.
65 Figure 25 - The path phase. An end-to-end path from a problem to a result is established.
5. Surround Results: After the first results appear in the canvas, a reorganization phase typically occurred in which the results suggest refinements of the original motivations and tangents of future inquiry. An important spatial construct in this phase is the notion of a 'scrap-pile', a transient area in which ideas can be temporarily stored while alternative organizations are being explored.
H-odng Pen
Figure 26 - The consolidation phase. Items are repositioned and boundaries are redrawn.
66 I found that certain aspects of spatial environments could be both a blessing and a curse for brainstorming. For example, space will not let you be ambiguous: placing a new item on an organized blackboard implies a commitment to what it is near. In a space where proximity has a particular meaning, the placement of an item is a semantic commitment. The committal nature of positioning an item can be a blessing because it forces you to be consistent and to represent the relationships between items explicitly. However, premature commitment is undesirable when it is unclear how an item fits into an existing context. One consequence of premature commitment is that I occasionally forgot where I had placed an item because I couldn't recall the reasoning I had used to put it there.
Another troublesome aspect of the standard blackboard is its opportunistic consumption of real estate. Over time, it becomes increasingly difficult to find open areas to place new items and plan for future additions; the image of an initially organized desktop grown monstrous over time is surely familiar to many. Time-consuming wholesale re-organizations of the blackboard were sometimes required. A blackboard that could automatically adjust its layout to manufacture space for a new item would be very desirable.
Conclusion
The designs presented in this chapter illustrate how a spatial metaphor can be applied to several real-world information spaces. In each of these studies, an information-intensive activity was recast as a navigation activity. Attaching key concepts from the domain to the LRPDP design elements then supported the corresponding navigation activity. These design exercises produced several useful design principles and techniques that can be usefully applied to other information spaces.
67 Chapter 5 Usability Studies in Spatial Navigation
There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. The other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult. - C.A.R. Hoare
Introduction
Formal evaluation is an important but understated aspect of information architecture. This chapter details four experiments designed to evaluate a simple set of hypotheses concerning the impact of the spatial metaphor on navigation. The first experiment examines the differences between spatial and page-based navigators of a web site. The remaining experiments gauge the value of landmarks, regions, and paths for navigation in a 2D aperture limited world.
The Digital Librarian Experiment Goals To evaluate the impact of a spatial metaphor on navigation, I prepared a usability study comparing navigation with and without a spatial view. The guiding questions for this experiment were:
Do subjects browse an information space differently when provideda spatial view? Does a spatial view enhance the memorability of an information space? Do subjects wayfind to target items more effectively when provideda spatial view?
Conditions I collected 98 informative text segments on dinosaurs from several popular Web sites [BBCWD], [ZoomD], [CybMu], [DisDn]. Each segment was distilled into a short verbal description ranging from approximately 50 to 300 words in length and converted into a standard hypertext format. I designed an information space from these segments using the following approach.
68 First, I identified six categories for the segments based on common organizational elements of the source Web sites. Each segment was placed into one of these six categories:
Classification - What is a dinosaur? How are dinosaurs named? How many dinosaurs were there?
Exhibit - Geological periods in which dinosaurs lived, the food chain in each period, images and descriptions of individual dinosaurs
Extinction - What is extinction? How long did it take for the dinosaurs to die? What is the asteroid theory?
Fossils - What is a fossil? What is paleontology? Descriptions of famous fossil sites
Anatomy and Behavior - How big were dinosaurs? How did they communicate?
News - Recent events in paleontology
Home pages briefly describing the content of the category were created for each of the six categories above. A navigation bar containing links to each of these main topic pages was added to the left margin of every page in the information space. In addition, each topic was associated with a distinctive color used around the border of every page within that topic; Figure 27 shows a sample page within the green exhibit topic.
The space was organized using a central tour path much like a physical museum exhibit. The purpose of this tour was to facilitate structured exploration of the site along natural dependencies between information segments. A primary tour path through the site was created to represent a coherent progression through the information; every item in the site was either on the primary tour path or accessible from it through a relatively short branch. The primary tour sequence and the first few items on the path within each topic are shown below:
1. Home - A single page describing the purpose of the exhibit. 2. Classification a. What is a dinosaur?
69 b. How are dinosaurs classified? c. How many dinosaurs are there?
d. ... 3. Exhibit a. The Mesozoic Era b. The Triassic Period c. Climate of the Triassic d. ... 4. Extinction a. What is extinction? b. Why did the dinosaurs go extinct? c. The Asteroid Theory d. 5. Fossils a. What is a fossil? b. What is paleontology? c. Where are fossils found? d. ... 6. News - This page contained single step links to five recent news items
On each page, two links to the next and previous items on the tour path were placed in a formatted area at the bottom of the page (see the lower section of the page in Figure 27 for an example).
The tour path was not a purely linear sequence through the site. Specifically, two types of branches were used to represent conceptual relationships between information segments. Content branches enabled users to explore conceptually independent areas (e.g. on the anatomy and behavior topic page, the user was given the option of exploring either an anatomy branch or a behavior branch). Detail branches provided more information on a particular item and then re- joined the main tour path (e.g. from a description of how dinosaurs are classified, the user may choose to learn more about the science of taxonomy before continuing to the next item). Lastly, the end of the tour linked back to the beginning to form a closed loop.
70 Subjects in the first group performed the tasks in a simplified classical Web browser. I will refer to these subjects as the P-subjects (i.e. page-viewers). The P browser used by these subjects displayed forward and back buttons but no URL location text box. P-subjects could navigate in two ways: by either following hyperlinks in the page or by using the forward and back buttons. A sample view of the site for P-subjects is shown below.
I
Carnivoires of the Triassic
at-eaters of the Triassic Penod included:
. Coelophysis - An small but adept killing machine . Postosuchus -The biggest predator of its time . Cynodont - A mammal like reptile . Peteinosaurus - An early pterosaur
-
Figure 27 - Browser view for P-subjects
71 T 7-
Subjects in the second group were given a browser augmented with a spatial view of the site; I will refer to these subjects as SP-subjects (i.e. spatial and page viewers). A sample view of the site for SP-subjects is shown in the figure below.
Carnivoires of the Triassic Aleat-eaters of the Triassic Period included: Coelooosis - An smal but adept killing machine "Postosuchus - The biggest predator of its tine "Cynodont - A mammal Ike reptile "Peteinosauros - An early pterosaur
Figure 28 - Browser view for SP-subjects
The spatial presentation method was an overhead, 2D view as described in Chapter 4. Every page in the site was mapped to a single labeled item in the spatial view. Every topic area was mapped to a region whose background color matched the associated border color of each page within that topic. Labels were positioned within the regions so that pages within topics were mapped to labeled items within regions. Links along the tour path were represented as directed arrows between labels in the view.
SP-subjects could navigate in four ways: by following hyperlinks in the page text, by using the forward or back buttons, by using the keyboard to translate and scale their spatial view relative to the mapping plane, or by animating the center of the spatial view to a label by selecting it with the left mouse button. The page and spatial views of the space were synchronized. Upon selecting a
72 hyperlink or using the forward or back buttons in the page view, the center of the spatial view was automatically animated to the location of the label for the destination page. Similarly, upon selecting a label in the spatial view with the left mouse button, the page view was updated to display the text of the corresponding page.
The browsers used by both the P and SP browsers time-stamped all subject navigation events and wrote them to a text file for later analysis.
Procedure A total of 18 subjects were used for the experiment, with nine subjects in each of the P and SP groups. The SP group contained 4 females and 5 males; the P group contained 5 males and 4 females. The table below displays the gender, age, and stated number of hours per week spent browsing the Web:
SP ID Gender Age Hours P ID Gender Age Hours SPI F 36 6 P1 M 29 20 SP2 F 27 2 P2 M 23 10 SP3 F 23 12 P3 F 25 1 SP4 M 31 30 P4 F 31 0 SP5 M 23 5 P5 F 20 1.5 SP6 F 30 1 P6 M 34 0 SP7 M 65 5 P7 F 64 2 SP8 F 29 0 P8 M 24 4 SP9 M 29 0 P9 M 45 20 Mean: 32.6 6.78 32.8 6.50
Figure 29 - Subject demographics for the browsing study
PracticeTask First, subjects were given a chance to become comfortable with their browser by practicing each of the available navigation methods in a small site containing nonsense items. The specific instructions read to the subject have been reproduced in Appendix A. Upon reporting that they were ready to continue, subjects were asked to perform a short set of navigation tasks in the
73 practice world to verify that they understood how to use each of the available navigational methods.
Browsing Task Next, subjects in both groups were asked to browse the site for fifteen minutes and to freely verbalize their thoughts while browsing. The specific instructions were as follows:
You will be exploring a web site designed to help people learn about dinosaurs. You will be given 15 minutes to explore the site. Your goal is to learn as much as you can about how the information about dinosaurshas been organized.Imagine that you will be a librarianfor this site: you do not need to memorize every fact, but you ought to know where the answers to questions are located.While you are browsing, talk about where you are in the site, what you are learning about its organization, and why you are making the choices you are making.
When the fifteen minutes had expired, subjects were asked to respond to the following task:
Please describe the organization of the site in as much detail as you can remember. Imagine I am a librarian in training and you are explaining to me how to find answers to questions.
The verbal protocol and responses for each subject were recorded to audiotape and later transcribed.
Mapping Task In the second task, subjects were asked to reproduce as much of the site as they could remember using a simple software tool. This tool provided a digital blackboard on which subjects could perform four operations: add a label to the blackboard, add a directed link between two labels on the blackboard, edit a label, or remove a selected label or link. A snapshot of this mapping tool is provided below. Subjects were given time to practice the four available operations. Upon reporting that they were comfortable with the tool, subjects were asked to perform a short series of tasks to verify their working knowledge before proceeding to the mapping task.
74 Figure 30 - Snapshot of the site-mapping tool
Subjects were instructed to reproduce as many pages and links between pages as they could recall and were given twenty minutes to construct their map. Upon completion, subjects were given an opportunity to explain any aspects of their maps that they felt might be difficult to understand.
Wayvinding Task In the final task, subjects were read a series of questions and asked to navigate as efficiently as possible to the single page within the site that contained the answer. The sequence of questions was selected at random given that at least one question was selected from each of the six categories.
Results SpatialSubjects Preferredto Browse Using the Spatial View SP-subjects were allowed to browse using both a spatial view and the standard hypertext view, yet SP-subjects showed a preference to navigate using the spatial view. The table below shows two measures of relative preference for the nine SP-subjects. A navigation event is defmed as a page hyperlink traversal, a single-step geometric transformation of the spatial view triggered by a
75 keystroke (up, down, left, right, zoom in, pan out), or the spatial selection of an item using the left mouse button. On average, 94.36% of the SP-subject navigation events were spatial events. Alternatively, the time spent per event is defined as the time after a navigation event and before a subsequent event. On average, 65.18% of a subject's time was spent navigating in the spatial view. The rows in the table below describe the total number of generated events (events), the total time (time), and the distribution of time (% time) and events (% events) between the spatial and page areas of the SP browsing interface.
SP1 SP2 SP3 SP4 SP5 SP6 SP7 SP8 SP9 Total Total: Events: 2101 508 565 793 521 472 870 629 242 6701 Time: 900 802 900 900 900 900 900 900 900 8002 Spatial Events: 2085 506 462 767 444 391 847 613 208 6323 %Events: 99.24 99.61 81.77 96.72 85.22 82.84 97.36 97.46 85.95 94.36 Time: 718 755 344 720 508 311 518 663 679 5216 %Time: 79.78 94.14 38.22 80.00 56.44 34.56 57.56 73.67 75.44 65.18 Pagze Events: 16 2 103 26 77 81 23 16 34 378 %Events: 0.76 0.39 18.23 3.28 14.78 17.16 2.64 2.54 14.05 5.64 Time: 182 47 556 180 392 589 382 237 221 2786 %Time: 20.22 5.86 61.78 20.00 43.56 65.44 42.44 26.33 24.56 34.82
Figure 31 - Distribution of browsing events and time spent by SP navigators
The time and event counts were tested for significance against a binomial random browser. For each spatial subject SP1-SP9, the binomial browser generated a paired sample with the same number of total events and the same total time as that subject. Navigation events were generated in either the page or the spatial view with equal probability (p-0.5) and an equal amount of time was spent on each navigation event (titotal time/number of events). F-Tests showed that the variances of the subject total time and event counts were significantly higher than those of the corresponding binomial model (f=0.043 for event distributions, f=1.42E-5 for time distributions). A paired, unequal variance T-Test showed the events generated by the spatial subjects to be significantly higher than the binomial baseline at a critical threshold of 10% (p-0.0666). The time
76 spent in the spatial view was significantly higher than the binomial baseline at a critical threshold of 5% (p=0.025).
An analysis of variance was performed for the total events generated, total spatial events, and total spatial time using the subject age and hours spent browsing per week as independent variables. The table below summarizes the fraction of the total variance explained by the independent variables (R2), the F-critical value at 5% significance, the F-observed value, the T- critical value at 5% significance, and the T-observed values for the age and hours per week.
R2% F-Crit F-Obs T-Crit T-Age T-Hours Total Events: 11.80% 5.143 0.4014 1.943 0.4266 0.8048 Spatial Events: 12.65% 5.143 0.4346 1.943 0.4128 0.8522 Spatial Time: 1.70% 5.143 0.0519 1.943 0.3200 0.0502
Figure 32 - Analysis of variance for spatial events
Overall, subject age and hours spent browsing per week explained very little of the observed variances and failed the F-test as well as individual T-tests on each factor. Given the wide range of plausible factors influencing browsing behavior (e.g. spatial versus verbal aptitude, educational level, rate of reading, previous familiarity with dinosaurs), this is perhaps unsurprising.
Spatial Subjects Explored SignificantIv More of the Site in Their Browsing The total number of page views (views), the total number of distinct page views (distinct), the fraction of page views that were distinct (%), and the total fraction of the site viewed (% site) are tabulated below for P and SP subjects.
77 Spatial SPi SP2 SP3 SP4 SP5 SP6 SP7 SP8 SP9 Tot Views: 35 73 112 96 165 133 57 71 116 858 Distinct: 22 64 58 60 69 46 34 46 75 474 %: 62.9 87.7 51.8 62.5 41.8 34.6 59.7 64.8 64.7 55.2 % Site: 22.4 65.3 59.2 61.2 70.4 46.9 34.7 46.9 76.5 53.5 Page P1 P2 P3 P4 P5 P6 P7 P8 P9 Tot Views: 155 204 121 97 102 121 47 66 96 1009 Distinct: 38 49 35 34 46 28 41 38 41 350 %: 24.5 24 28.9 35 45.1 23.1 87.2 57.6 42.7 34.7 % Site: 38.8 50 35.7 34.7 46.9 28.6 41.8 38.8 41.8 39.7
Figure 33 - Total page views and distinct page views for P and SP subjects
Spatial subjects visited significantly more distinct pages than their non-spatial counterparts (p = 0.0235). The spatial subjects visited about 53% of the total site on average, while the non-spatial subjects saw less than 40% of the site. Although spatial subjects generated more total page views on average as well, this difference was not significant (p = 0.2138).
The probability of visiting a given page for a given subject was estimated as the total number of visits to that page divided by the total number of visits. Rank orderings of the log negative page visit probabilities for P and SP subjects are plotted below.
78 L 7 27 7- son
Rank Ordering
3.2500
2.7500
2.2500 S- Page
0 '5 - Spatial S1.7500
1.2500 I
0.7500
Rank
Figure 34 - Page probability rank orderings for P and SP browsers
The rank ordering for P subjects was more strongly peaked and falls off more quickly with increasing rank, thereby implying that page-based browsers concentrated more time on a smaller fraction of pages. One clear explanation for this is the presence of path dependencies in the hypertext graph: if the only path to page B is through page A, then the frequency of visiting B must be at least that of A.
Another factor in the relatively low fraction of the site explored by P subjects may be a hesitation to follow long paths into the site. I constructed a baseline model using a Markov random browser. At each page, this browser selected one of the outgoing links or the back button based on a uniform distribution. The Markov browser was used to derive page occupation probabilities in the steady state for every page in the site. The plot below displays the page occupation probability as a function of its shortest path distance from the home page. The first two curves in the right legend ('P-Subjects', and 'Markov') correspond to the aggregated browsing samples of the P browsers and the Markov browser. The 'Site' curve represents the fraction of pages at a given shortest-path distance from the home page (i.e. the occupation probabilities for a browser that
79 could visit any page at any time with uniform probability). The last curve ('SP-Subjects') represents the aggregated samples of the spatial subjects.
Expected Site Penetration
0.8
0.7
0.6
0.5 -- P-Subjects
--- Markov 0.4 CL-U| -A--Site 0.3 _SSubjects
0.2
0.1
0 - --U- 0 1 2 3 4 5 6 7 8 9 Path Length
Figure 35 - Expected browsing penetration depth
The center of gravity of the site appears at a distance of 4.01 links from the home page. The left- most peaks in the P, SP, and Markov distributions correspond to the relatively high fraction of visits to the six main category pages that appeared in the navigation bar. The expected penetration depth of the P subjects (2.35) was almost twice that of the random browser (1.16), but only half that of the expected shortest path distance to a page in the site. As a result, P-subjects on average explored less than 40% of the site. On the other hand, the distribution for spatial browsers closely mirrors the distribution for the site; this is to be expected, since spatial browsers were able to select any item in their visible viewing area.
An analysis of variance in the total number of page views, distinct views, and time spent per page was performed against subject age and hours spent browsing per week. The results are shown in the table below.
80 R2 % F-Crit F-Obs T-Crit T-Aae T-Hours SP-Subjects Total Views: 28.97 5.143 1.2235 1.943 -0.0569 -1.564 Distinct Views: 34.75 5.143 1.598 1.943 0.1699 -1.77
P-Subjects Total Views: 46.01 5.143 2.5562 1.943 1.374 -1.897 Distinct Views: 11.41 5.143 0.3866 1.943 0.8495 -0.2924
Neither age nor the hours spent browsing per week explained a significant fraction of the variances for the page view measurements.
Spatial Subjects Recalled More of the Site In the second task, subjects were asked to reproduce as many pages and links between pages as they could remember from their browsing experience. I will use the word label to denote an element in a subject map used to represent a page, and the word arrow to denote a directed line in a subject map used to represent a hyperlink. Every label in every subject map was placed into one of six categories:
Page Hits - Labels that correspond to an existing page in the site
Positive Wildcards - Labels indicating that the subject correctly recalled that a page was present but could not recall its contents. The validity of the wildcard is inferred from its relationship to other items in the map. For example, a subject might place a linked positive wildcard labeled 'X' next to the label for an accurate page to indicate that they remembered a neighboring page but could not recall its subject. If such a page actually existed, the label 'X' would be considered a positive wildcard.
Page Generalizations - Labels that either corresponded to either the contents of more than one page in the site or to broad generalizations of single page topics. For example, the label 'where dinosaurs lived' would be a page generalization because dinosaur habitats were described in several pages throughout the site.
81 Page Specializations - Labels corresponding to specific facts or fragments within a more general topic page. For example, a label such as 'some dinosaurs had beaks' would be a specialization of the page describing how dinosaurs are related to birds.
Page Misses - Labels that did not correspond to any page in the site. Ambiguous or incomprehensible labels were categorized as misses.
Negative Wildcards - A wildcard that did not represent a valid structural relationship between pages in the site. For example, if a subject placed a label 'X' in a linked path between two accurate labels when no such path existed in the site, then the label 'X' would be considered a negative wildcard.
Arrows in the maps were placed into one of the following three categories:
Link Hits - An accurately directed arrow between two accurate laels or positive wildcards indicating a valid hyperlink.
Path Generalizations - An accurately directed arrow between two accurate labels or positive wildcards indicating a valid connectivity relationship between two pages not more than two links deep. The threshold on the path length is necessary because the site is fully connected.
Link Misses - Arrows that did not correspond to a valid hyperlink in the site.
Scores for the spatial and non-spatial maps are tabulated below. The rows from top to bottom denote the total number of distinct page views for each subject (views), the total number of labels in their maps (labels), the percentage of map labels that were either page hits or positive wildcards relative to the number of distinct page views seen while browsing (% recall), the percentage of the total site that was accurately mapped (%site), the total number of mapped links (links), and the percentage of mapped links that were link hits (%+).
82 SP SPi SP2 SP3 SP4 1SP5 SP6 SP7 SP8 SP9 Tot Views: 22 64 58 60 69 46 34 46 75 474 Labels: 13 34 25 58 53 18 7 29 41 278 % Recall: 50 45.3 32.8 75 10.1 23.9 20.6 58.7 45.3 40.2 % Site: 11.2 29.6 19.4 45.9 7.14 11.22 7.14 27.55 34.69 21.54 Links: 10 37 25 65 64 17 7 30 41 296 % +: 50 59.5 48 60 1.6 29.4 100 43.3 61 43.58 P P1 P2 P3 P4 P5 P6 P7 P8 P9 Tot Views: 38 49 35 34 46 28 41 38 41 350 Labels: 13 24 16 15 23 10 19 14 31 165 % Recall: 29 40.8 22.9 35.3 37 28.6 26.8 26.3 46.3 32.5 % Site: 11.2 20.4 8.2 12.2 17.4 8.2 11.2 10.2 19.4 13.2 Links: 12 23 19 9 23 4 19 25 28 162 % +: 50 56.5 15.8 55.6 34.8 25 15.8 56 32 3.
Figure 36 - Comparison of map accuracies for P and SP subjects
Spatial subjects mapped more pages, recalled more pages, reconstructed more of the site, and represented a higher fraction of accurate links on average. F-Tests on the number of accurately mapped pages and links indicated significant differences between the spatial and non-spatial variances (p=6.5E-3, 1. 1E-2 respectively). The total number of accurately mapped pages and links were significantly higher spatial subjects, as measured by a single-tailed, unequal variance T-Test with a threshold of 10% (p=0.057, 0.058 respectively). However, although spatial subjects had higher recall (i.e. the total number of accurately mapped pages divided by the total number of distinct page views), the difference was not significant (pO. 158).
An analysis of variance was performed on the total labels, total links, total accurate labels, percent recall, total accurate links, and link percent accuracy against age and hours spent browsing per week. The results are shown in the table below.
83 12 F-Crit F-Obs T-Crit T-Aie T-Hours Spatial: Total Labels: 54.14 5.143 3.54 1.943 1.61 -2.05 Accurate Labels: 33.48 5.143 1.51 1.943 1.42 -0.94 Recall %: 26.62 5.143 1.09 1.943 1.39 -0.45 Total Links: 49.70 5.143 2.96 1.943 1.53 -1.83 Accurate Links: 38.29 5.143 1.86 1.943 1.86 -0.45 Accurate %: 60.84 5.143 4.66 1.943 0.63 3.01
Non-Spatial: Total Labels: 21.67 5.143 0.83 1.943 1.19 0.41 Accurate Labels: 23.17 5.143 0.90 1.943 1.33 -0.32 Recall %: 23.72 5.143 0.93 1.943 1.37 -0.15 Total Links: 10.28 5.143 0.34 1.943 0.83 -0.09 Accurate Links: 30.93 5.143 1.34 1.943 1.13 -1.27 Accurate %: 37.22 5.143 1.78 1.943 0.99 -1.68
Age and hours spent browsing per week did not explain a significant fraction of the variance for any measurement (the observed F-values in column three are all less than the critical value in column two). The hours spent per week did appear to have a predictive relationship to the total labels generated and the fraction of accurate links for the spatial subjects. Overall however, the variance in recall within this sample appears to depend largely on other factors. Given the wide variance in subject recall ability, a much larger sample set should be run to better test the memorability hypothesis.
84 Figure 37 - High-level view of the spatial layout of the dinosaur site
The maps drawn by SP and P subjects exhibit interesting qualitative differences. The high-level map structure of the site as visible to the SP subjects is shown in the figure above. Representative P and SP maps are included below (maps for all subjects have been reproduced in the Appendix). Most of the P maps were strictly hierarchical or only loosely connected. None of the P browsers noticed that the site was organized in a loop, and much of the branch structure appears to have gone unnoticed. Given the strong evidence that the category home pages served as anchors for P subjects (e.g. they are all at the top of the rank ordering of page hits), this distorted view of the site is consistent with the 'Lost in Hyperspace' distortion discussed in Chapter 2 (see Figure 3).
85 - I I - .- . a?- - - - I - __ I - .- I-, - -__ - - __ __ , __ - - - :_ ------Rnmnffl
Jm1
Figure 38 - A representative map for a P subject
Six of the nine maps for the SP subjects noted the looping structure of the site. In addition, SP maps provide some evidence that the spatial view served a mnemonic role. In many, but not all cases, spatial maps were laid out to match the layout of the actual spatial view (see the map below). Furthermore, the total number of positive wildcards was significantly larger for the spatial group (59) than for the non-spatial group (12) (p-0.026), indicating that spatial subjects were more frequently able to represent the location of existing items even though they often could not recall their identity.
86 "M - wz ,
Tn r -..... AM
Figure 39 - A representative map for SP subjects
The most striking examples of the mnemonic role of the spatial view appears for an SP subject who claimed to not be able to recall any pages from the site. The map for this subject, shown below, represents only the main category pages and a coarsely connected looping network. Although unable to accurately identify any of the pages, this subject's map accurately reproduced the high-level main loop and category pages in the site. Similarly, a second subject who also expressed difficulty in recalling pages was also able to represent the main topic pages and the looping structure of the site (see second Figure below).
87 IN 17 Va
FIgr40-ASPsbetwocudntrclaypgs
88 Figure 41 - An SP subject who had difficulty recalling any pages
SpatialSubjects SearchedMore Accurately In the final task, subjects were asked to locate the answers to questions as efficiently as possible. The table below charts the total questions asked (questions), the total number of answers found (found), the total number missed (missed), the total time taken (time), the total time taken for answers found (+ time), and the average time per answer found (time/+).
89 SP SP. SP2 SP3 SP4 SP5 SP6 SP7 SP8 SP9 Total Questions: 15 13 15 15 15 15 15 15 15 133 Found: 13 12 14 15 14 13 12 15 14 122 Missed: 2 1 1 0 1 2 3 0 1 11 Time: 1070 600 565 492 558 717 794 338 449 5583 + Time: 684 180 565 492 370 379 204 338 305 3517 Time /+: 52.16 15 40.36 32.80 26.43 29.15 17 22.53 21.79 28.83 P P1 P2 P3 P4 P5 P6 P7 P8 P9 Total Questions: 15 13 15 15 15 15 15 15 15 133 Found: 11 11 9 8 11 10 10 12 13 95 Missed: 4 2 6 7 4 5 5 3 2 38 Time: 782 952 962 1548 938 1310 989 1119 782 9382 + Time: 173 499 200 329 250 425 317 641 367 3201 Time /+: 15.72 45.36 22.22 41.13 22.73 42.5 31.7 53.42 28.23 33.67
Figure 42 - Impact of a spatial view on the accuracy and efficiency of search
Spatial seekers found significantly more answers (p = 0.000254). Although the average time per positive trial was slightly lower for spatial searchers, this difference was not significant (p = 0.39).
Spatial subjects appeared to pay relatively little attention to hyperlinks in the page text while wayfinding. As discussed in an earlier section, SP subjects spent significantly more time navigating in the spatial view. In addition, on two trials in the wayfinding task, the answer to the following question could be found by traversing a single hyperlink in the body of the main text. P subjects as a group found 14 of the 18 possible single-step answers. SP subjects found none of them, choosing instead to find the answer by navigating in the spatial view.
Questions that displayed the largest performance differences between the P and SP groups illuminate the difficulties P subjects had with the path structure of the site. Only three of the nine P subjects were able to find the answer to the first question: 'how do scientists estimate the intelligence of a dinosaur?'. Eight of the nine SP subjects successfully found this answer. The reason may be that the answer appeared on a page four links away from the home page. Along the path to the answer, P subjects would have to navigate past a one main content branch and one
90 detail branch. Similarly, four of the fourteen questions displayed a performance differential of three between the P and SP groups (i.e. 8 of the 9 SP subjects were able to find the answer, but only 5 of the 9 P subjects were able to find the answer). The distances from the home page for these four pages were 5, 8, 5, and 4, which are all greater than the average penetration depth into the site observed during browsing (2.35). The shallow browsing depth into the site coupled with the poor wayfinding performance for targets beyond three links from the home page suggest that P browsers were hesitant to follow long paths into the site. Furthermore, because P browsers did not appear to search systematically for targets (e.g. breadth-first), the number of branch points en- route to the target is likely to be a significant factor in wayfinding performance; this hypothesis should be further tested in a later experiment.
As discussed in Chapter 3, the aperture problem provides an important conceptual link between navigation in physical and virtual worlds. In the following series of experiments, the usability consequences of navigation in an aperture-limited world are examined in more detail.
The Aperture Experiments
Goals To observe how users navigate in worlds much larger than their field of view, I devised a series of three experiments set in a virtual landscape. Environmental psychology suggests that people use landmarks, regions, and paths as mental primitives to navigate in complex environments. The goal of the landscape experiments was to verify the impact of these primitives on navigation in a simple class of virtual worlds and to cast the results into prescriptions for information architecture. The guiding questions were:
How useful are landmarks,paths, and regions to navigation in an aperture-limited virtual environment?
Do the ways subjects navigate in these worlds suggestprinciples for the design of virtual environments?
I examined a two-dimensional, overhead metaphor in the aperture experiments (see Chapter 4). In this interface, subjects navigate left, right, up, or down at a fixed scale and orientation above the world. This is both the simplest and most widely used two-dimensional spatial interface. Although very simple, this world retains the essential feature that the view area is smaller than the
91 size of the underlying world. As such, the overhead interface retains the essential connection to the aperture problem and offers a useful point of departure.
Conditions Subjects in the landscape experiments were asked to perform tasks in four worlds, designated LRP 100, Z100, LRP 1000, Z1000; these worlds are shown in the figures below. Each world was populated with identical blue items that were randomly positioned. LRP 100 contained 100 items and was designed using landmarks, regions, and paths (LRP). The region backgrounds were colored counter-clockwise from brightest to dimmest. The landmarks are slightly larger, yellow items located near the center of each region. The paths run roughly along the diagonals of the regions. The central white squares in these figures represent the area of the view port relative to the total canvas area. Z100 is LRP 100 without landmarks, paths, or regions. The relative area of the view port, the total number of blue items, and the locations of the blue items in LRP 100 and Z100 are identical. LRP 1000 and Z1000 are larger versions of LRP100 and Z100 containing 1000 blue items. The relative view port area is an order of magnitude smaller in these worlds.
Each landscape experiment was administered with the same procedure. First, each subject was read a series of instructions describing the interface and the task they would perform; instructions for each experiment have been reproduced in Appendix A. Each subject was then given the chance to become comfortable with the task and interface by performing 10 trials in a small practice world. After the practice run, if subjects stated that they were comfortable with the interface and the tasks they were being asked to perform, they proceeded to the primary trials.
Subjects first performed the task in LRP 100, then were given a 10-minute break, and then performed the task in Z100; the trials used in LRP 100 and Z100 were identical. In a second session, subjects performed the task in LRP1000, were given a 10-minute break, and then performed the task in Z1000; as in the smaller worlds, the trials used in LRP 1000 and Z1000 were identical. Finally, subjects were asked these questions:
1. Order the worlds you performed the task in from easiest to hardest. 2. How did you perform the task in LRP 100? 3. How did you perform the task in Z100? 4. Was there any difference between the way you performed the task in LRP 100 and in LRP1000?
92 5. Was there any difference between the way you performed the task in LRP 100 and in LRP1000?
The aperture experiments were performed in a Windows application running on a PC. All interactions with the application, including key and mouse events and associated translations of the viewpoint, were time-stamped and recorded to a file for later analysis.
93 Figure 43 - Overhead view of LRP100
Figure 44 - Overhead view of Z100
94 Figure 45 - Overhead view of LRP1000
Figure 46 - Overhead view of Z1000
95 Experiment 1: Estimating Current Location
The first experiment tested the effect of landmarks, paths, and regions on subject ability to estimate the current location of their viewpoint relative to the boundaries of the landscape. Six subjects, two females and four males, participated in this experiment.
Procedure Subjects were presented with an overhead view of a landscape and given a maximum of 3 minutes to examine it; this view was presented only once. Next, a series of 50 trials was administered. A trial consisted of a series of animated translations of the viewpoint followed by a request to estimate the current location of the view:
* The viewpoint was automatically navigated to a blue item in the landscape according to a pseudo-random sequence. * Subjects were then asked to touch the highlighted blue item at the center of the screen. The number of animations per trial was generated from a uniform distribution between one and four. * A dialog box was presented asking the subject to touch the current location of the viewpoint; this dialog is shown below. The boundaries of the landscape were drawn, but no other items from the landscape were provided. The dimensions of the dialog area in device units matched those of the overhead view shown to subjects at the beginning of the experiment. Subjects were allowed to reposition their view by pressing the left mouse button and no explicit time limit was enforced. * When satisfied with their estimate, subjects clicked OK and were then shown the actual location of the view window highlighted in red. Upon clicking either OK or Cancel, a new trial was initiated.
Subjects were given a button labeled 'Where am I?' at the bottom of the application window. If subjects pressed this during the sequence of animations, the same dialog box used to input the position estimate was presented and the current location of the view was drawn in red.
96 Figure 47 - The dialog shown to subjects at the conclusion of a trial. The subject's estimate was drawn in yellow and the actual location of the viewpoint was drawn in red.
Results Subjects estimated their position more accuratev when explicit features were present The table below charts the mean and variance of the per-trial estimation error. Columns represent the six subjects and the average across all subjects. Rows list the landscapes in the order they were tested. A paired, single tail T-test was used for significance testing.
A trial rejection criterion was introduced to account for subject use of the 'Where am I' button. Because subjects were allowed to press the 'Where am I' button at any point prior to a position estimate, some trials were either degenerate or asymmetric. A trial was termed degenerate if the subject had pressed the 'where am I' button just before being asked to state the view location. A trial was termed asymmetric if the number of view animations prior to a position estimate was not the same because the subject pressed the 'where am I' button in either the control or the designed world but not in both. Degenerate and asymmetric trials were excluded from the summary data provided below. The number of valid trials per subject is listed in the table above the T-test.
97 1 2 3 4 5 6 Av2 LRPJO0 36.292 22.555 16.931 33.246 22.977 31.076 27.036 a 21.400 13.373 8.170 18.510 23.34 18.364 18.328 Z1G 55.307 50.212 38.354 39.256 67.883 54.406 50.632 a 36.974 30.348 27.965 11.496 40.979 32.043 32.781 Trials 50 50 45 14 18 50 227 T-Test 0.001 1.72E-8 6.93E-6 0.134 0.0003 2.23E-6 7.135E-21
LRPOOO 30.650 21.037 30.337 38.390 42.211 30.413 29.380 a 28.867 15.266 21.932 15.433 43.265 22.378 24.468 ZOGO 73.192 53.008 47.079 46.046 69.260 54.253 57.933 a 35.429 25.863 25.864 22.371 32.147 33.734 31.785 Trials 50 48 34 12 12 41 197 T-Test 2.10E-10 2.75E-9 0.007 0.168 0.054 0.0004 1.551E-20
Figure 48 - Error magnitudes in device units for position estimates made in the four test worlds
The pooled trials, shown in the far right column, show a significantly lower mean squared error in the position estimates made in the designed worlds LRP 100 and LRP 1000 compared to the featureless worlds Z100 and Z1000 (i.e. 27.036 << 50.632, 29.380 << 57.933). This effect appears in the per-subject results as well.
Subjects 4 and 5 used the 'Where am I' button very frequently; less than 1 in 4 trials passed the criterion for rejection; this accounts for the failed individual t-tests for these subjects.
Subjects reportedthe task was easier when features were present All six subjects reported that the worlds with features (LRP100, 1000) were subjectively easier to perform the task in than the featureless worlds (Z 100, 1000). Furthermore, five of the six subjects reported that the smaller worlds were easier than the larger worlds; the one exception stated that LRP 1000 was easier than LRP 100 because he had become more comfortable with the task.
Discussion A common error occurred across several subjects. The contrast between the background colors of the left two regions in LRP 100 and LRP 1000 was rather low. As a result, many subjects incorrectly guessed which region they were in when asked to estimate their position within one of
98 these two regions. This class of errors indirectly supports the hypothesis that subjects were using regions to estimate their position. In addition, the errors suggest a design pitfall to avoid:
The Salient Background Principle - Maximize the visible differences between regions.
Otherwise, the confusions that result may be worse than not providing regions at all.
When asked how they performed the task in the featureless worlds, most subjects reported using a path integration strategy: they assumed that the speed of the view was constant between trials and waited for edges and corners to appear in the view (effectively re-calibrating their integrator). Two subjects reported trying to memorize a cluster of blue items near the center of the landscape as a virtual landmark. These verbal descriptions reinforce a simple design principle:
The Frequent Feature Principle - Provide explicit features every few views.
Make features explicit or subjects may try to invent them anyway. Provide them every few views so that subjects need not integrate noisy estimates of their movement over long distances.
Features in the LRP worlds were regularly spaced and this regularity appeared to be important to subjects when estimating position. For example, one subject estimated her position in the dialog box using the mouse pointer to mark off regular distances from the boundaries of the landscape: she moved the pointer to the center of the dialog box, measured half the distance to the edge nearest to her view, and adjusted her estimate from this location. The usefulness of regular dimensions in estimating position yields an important design principle:
The Small Divisor Principle - Position and scale items in the space to divide its extent into a small number of regularly sized units
99 Experiment 2: Returning to a Landmark
The second experiment tested the effect of landmarks, regions, and paths on subject ability to navigate back to a known location. In this task, red, green, and purple landmarks were added to each of the test landscapes; the figure below shows the overhead view of the Z 100 landscape with the added landmarks. Six subjects, four females and two males, participated in this experiment.
Figure 49 - The Z100 landscape with added landmarks
Procedure Subjects were presented with an overhead view of a landscape and given a maximum of 3 minutes to examine it; this view was presented only once. Next, a series of 50 trials was administered. A trial consisted of a series of animated translations of the viewpoint, followed by the random selection of one of the three landmarks, followed by a request to return to and touch the selected landmark. The sequence of animations was generated in the same manner as the estimate position experiment. During the animations, each of the landmarks was camouflaged as an ordinary blue item. After the sequence of animations, a target landmark was chosen at random according to a uniform distribution, and a line of instruction text appeared in the lower left corner of the view window instructing the subject to return to and touch the given target landmark. At
100 this point, the target landmark was returned to its distinguished color. The subject was allowed to navigate the view window left, right, up, or down using the arrow keys. Upon returning to the target landmark and touching it, the landmark was once again camouflaged to blue and a new trial was initiated.
The subject was given two buttons at the bottom of the application window, labeled 'Where am I?' and 'Where are the Landmarks?' Pressing the 'Where am I?' button presented a dialog box identical to that used in the estimate position experiment; this box displayed the boundaries of the landscape and drew the current area of the viewport in red. Pressing the 'Where are the Landmarks?' button displayed the same dialog with the locations of the three landmarks drawn in rather than the location of the viewpoint.
Results
Subjects returned to a familiar location much more efficiently when features were present The average number of mis-steps per trial is charted below; a mis-step was defined as a navigation of the view window that increased the distance between the view center and the target landmark for the trial. Columns represent the six subjects and the average across all subjects. Rows list the landscapes in the order they were tested. In addition to the mean and standard deviation, the number of times the subject pressed the 'Where am I' button (labeled Nviews) and the number of times the subject pressed the 'Where are the Landmarks' button (labeled Nlmark) are shown for each landscape. A paired, single tail T-test was used for significance testing.
101 1 2 3 4 5 6 AM~ LRPIOO p 7.42 1.96 0.26 9.66 3.12 18.34 6.793 a 15.714 8.236 0.694 13.924 11.48 37.69 19.36 Nviews 20 0 0 0 1 0 21 Nimark 19 0 0 0 4 0 23 Z1G 58.06 47.54 43.24 127 36.36 45.98 59.70 a 53.642 31.763 30.582 150.575 26.83 36.33 76.10 Nviews 5 0 0 0 11 0 16 Nlmark 7 0 0 0 4 0 11 T-test 1.81E-9 6.20E-14 1.25E-13 8.36E-7 2.39E-11 0.0001 3.39E-27
LRPOOO p. 31.44 33.46 8.08 88.38 12.02 63.56 39.49 a 52.675 93.959 23.498 223.94 21.74 143.32 120.24 Nviews 16 0 0 3 3 1 23 Nlmark 16 1 0 2 4 1 24 Z1O p 169.28 450.34 288.2 549 162.02 512.54 355.23 a 169.411 500.848 307.161 459.60 125.63 522.46 409.78 Nviews 113 9 54 1 79 81 337 Nlmark 38 5 34 1 7 0 85 T-Test 1.99E-7 1.835E-7 2.48E-8 2.46E-8 3.OOE-11 2.58E-7 1.09E-31
The table shows that subjects made significantly fewer missteps in the LRP worlds; in the worlds with 1000 elements, the difference is almost an order of magnitude.
Subjects reportedthe task was easierwhen features were present All subjects stated that the featured worlds (LRP 100, 1000) were easier to perform the task in than the corresponding featureless worlds (Z100, 1000).
Discussion Several subjects were able to navigate the view in the Z1000 world quite close to the target location, yet took many steps to find its exact location ('I know it's around here somewhere, but I'm not sure exactly where'). This effect has a simple explanation: the further away a target is from one's current location, the more pronounced the effect of any error in the estimate of its direction. As such, targets several view-lengths away at an arbitrary angle were difficult to find, particularly in the larger featureless world. This effect suggests a design principle:
102 The Alignment Principle - Align landmarks along natural directions of movement
With aligned landmarks, navigators will not be forced to estimate relative orientation.
Experiment 3: Re-Orienting
The third experiment tested the effect of landmarks, paths, and regions on subject ability to orient after being teleported to a random location. Six subjects, two females and four males, participated in this experiment.
Procedure Subjects were presented with an overhead view of a landscape and given a maximum of 3 minutes to examine it; this overhead view was only presented once. Next, a series of 50 trials were administered. A trial consisted of a discrete jump ('teleport') of the view window to a random location in the landscape, followed by an opportunity to navigate the view window, followed by a request to estimate the current location of the view window. After teleportation, the subject was able to navigate the view window left, right, up, or down using the arrow keys. Once the subject was confident that they knew the current location of the view, they were asked to press a button at the bottom of the application window labeled 'I Know My Current Location'. After pressing this button, a dialog box identical to that used in the estimate position experiment was presented. As in the estimate position experiment, the actual location of the view window was drawn in red after subjects finished their position estimate.
Results Subjects took fewer steps to make an accurateposition estimate when features were present The table below plots the number of steps taken after teleportation and prior to making a position estimate, and the average error of the resulting estimate per subject.
103 1 2 3 4 5 6 A6V2 LRP100 Steps 7.22 25.64 6.7 7.36 9.06 23.39 13.31 Error 31.42 12.03 26.24 38.63 32.37 20.78 26.94 Z1 Steps 85.84 78.68 70.92 67.66 47.86 78.86 71.9 Error 32.83 2.57 3.40 25.87 17.56 4.43 14.45 T-Test Steps 2.70E-12 1.08E-17 7.26E-25 7.98E-23 1.65E-16 4.34E-20 2.06E-86 Error 0.382 0.002 3.56E-5 0.05 0.02 0.0002 7.17E-8
LRPJ000 Steps 22.62 105.6 52.34 63.02 47.4 82.72 62.28 Error 49.56 4.04 10.05 34.56 19.06 6.08 20.56 Z1G Steps 210.64 212.7 214.02 213.44 162.44 209.22 203.74 Error 39.60 1.04 1.60 13.44 14.76 1.95 12.07 T-Test Steps 1.74E-12 9.91E-15 6.27E-22 5.39E-18 3.74E-17 6.35E-14 6.41E-79 Error 0.146 3.18E-8 7.37E-14 0.01 0.12 1.48E-9 1E-4
Figure 50 - Number of steps and resulting error for post-teleportation position estimates
The total number of steps taken was significantly smaller for subjects in LRP worlds. However, the resulting position error was also significantly larger. The reason for this is that all subjects performed the estimation task in the featureless worlds in the same way: by navigating to an edge, and then following the edge to a corner. As a result, subjects were able to make very accurate position estimates in the featureless worlds - average errors for some subjects were less than 10 device units for several subjects. In contrast, subjects in the LRP worlds were often able to estimate their position accurately based on a single view.
Subjects reported that the task was easier in the featured worlds All subjects stated that the task was easier to perform in each LRP world than in its featureless counterpart.
Lessons From the Aperture Experiments
The first question of the Aperture Experiments was:
Can primitives such as landmark,path, and region enhance user ability to perform common navigationtasks in a virtual environment?
104 The results strongly suggest that the answer is yes: landmarks, paths, and regions can enhance user ability to estimate their current position, to return to a familiar location, and to re-orient themselves.
The second question of the Aperture Experiments was:
Do the ways subjects perform these tasks suggest principlesfor the design of virtual environments?
Reflection on the nature of the Aperture Problem suggests three basic design principles for aperture-limited spatial environments:
The Distinctive View Principle - Make views as distinctive as possible. Avoid layouts whose local views are visibly indistinguishable.
The Distinctive View principle is an important requirement for local views to connote global position. As illustrated in the figure below, local views of a uniform grid layout are highly ambiguous, whereas in a random layout, chances are good that no two views will be the same. In Lynch's seminal work on urban planning, Boston represents a city with heterogeneous, highly distinctive views, contrasted against the regular grid structure of Jersey City [Lynch60].
U
I. I I
Figure 51 - Local views of a random layout (left) are distinctive but not locally predictable. Local views of a regular grid (right) are not distinctive but are locally predictable.
105 The Local Imagability Principle - Seek to structure the layout such that adjacent views are predictable from their neighbors.
This principle supports inference in the vicinity of the current view. Whereas the purely random layout illustrated above is more distinctive than the grid layout, the grid layout is more locally predictable than the random layout because a user can infer the spatial periodicity of the elements. A good spatial layout must balance this tradeoff between predictability and distinctiveness.
The Global Imagability Principle - Seek to structure the layout such that local views can be easily situated within a global structure.
This principle corresponds to Lynch's original notion of 'imagability': the ability of an urban navigator to form a coherent mental representation of the city whole from local views of its parts [Lynch60]. Hierarchical representation appears to be an important aspect of global imagability. For example, we imagine the United States to consist of a group of states, which in turn contain counties, cities, neighborhoods, and so on. In the illustration below, the random layout has very low imagability, whereas the image of the smiling, winking face is highly distinctive, locally imagable, and globally imagable.
*r-- r-
I U El E I..
Figure 52 - A random layout (left) has low global imagability. The image of a smiling, winking face (right) is highly imagable from local views.
106 In addition to the three principles described above, observation of subject behavior in the landscape experiments suggested additional principles for the design of spatial environments. These principles have been summarized below.
The Salient Background Principle - Maximize the visible differences between regions, or the confusions can be worse than not providing regions at all
The Frequent Feature Principle - Provide explicit features every few views, or navigators may try to invent them anyway
The Small Divisor Principle - Position and size items in the space to divide its extent into a small number of regularly sized units.
The Alignment Principle - Align landmarks along natural directions of movement to prevent subjects from having to estimate relative direction. Otherwise, orientation errors can accumulate over long distances.
107 Chapter 6 Design Principles
Those are my principles. If you don't like them I have others. - Groucho Marx
This chapter summarizes the design premises and principles applied in this thesis. Each principle has been stated in a prescriptive form (as an action to undertake or a pitfall to avoid). In addition, effort has been made to specify each principle (e.g. the horizon principle) at a level of abstraction more specific than general HCI principles (e.g. make choices visible [Normn9O]), and more general than specialized hypertext design guidelines (e.g. avoid textured backgrounds because they obscure text and links [WSTSk]).
Justify the Metaphor - To be effective, any metaphor ought to match the structure of the information space. The following simple tests can help to determine whether or not the spatial metaphor is appropriate:
The Multiple Access Test - If there are many ways to get from here to there, consider a spatial metaphor. Example: planning a wedding
The Contextual Test - If decisions depend on more than two items at a time, consider a spatial metaphor. Example: project management
The Habitat Test - If the supported activity occurs infrequently, a spatial metaphor may not be worthwhile. Example: the engineering statistics handbook
Capture and Communicate Knowledge of the Domain - This thesis has championed a knowledge-based approach to information architecture rather than a purely automated approach based on syntactic properties of general data structures. This approach proceeds from the following principle:
108 The Knowledge Navigation Principle - The navigability of an information space derives from the specific domain knowledge embedded within its organization. Example: The MIT Vision Space
The LRPDP elements provide the vocabulary for expressing that domain knowledge.
General Navigation Principles - These principles apply to the navigation process in general, and apply to both hypertext and other navigation metaphors. I have argued that one reason the spatial metaphor and the LRPDP elements can be effective is that they naturally implement many of these principles:
The Anchor Principle - Enable users to easily orient to a small set of salient locations. Example: navigation bars, spatial landmarks
The Transition Principle - Make organizational transitions explicit. Example: label links that leave the site, spatial regions
The Incremental Commitment Principle - Give users more than one level of detail to examine before deciding whether or not to pursue a given option. Example: display an extended summary or list of exemplary items on mouse-overs
The Horizon Principle - Give navigators a salient destination to navigate towards. Example: a virtual tour
The Visible State Principle - Provide visible feedback on the user's current state relative to where they have been and where they are going. Example: show the path from the root to the current page in a tree-structured site
109 The Main Street Principle - Provide a central orienting path through the space. Example: a chronological organization
The Visible Destination Principle - Tell navigators where a path will eventually take them. Example: make the endpoints of the path visible
The Measured Extent Principle - Tell navigators how long a path will last. Example: display the number of steps remaining along the path
Principles for Spatial Tours - A tour is a useful technique for introducing a navigator to the organization of a site. In designing a tour:
The Situated Action Principle - Teach users in the same place they use what they learn.
The Active Learner Principle - Include stops where users are asked to perform a small navigation task based on what they have learned.
The Exhibit Principle - Reinforce the abstractions of the space with exemplary individual items.
The Homing Principle - Follow a tour trajectory that enables a familiar landmark to be seen so that users can relate new items to ones that are more familiar to them.
The Footstep Principle - Distinguish items that have already been visited from novel items.
110 Layout Principles - The positions of the information items ought to respect the aperture problem. Keep the following points in mind:
The Distinctive View Principle - Make views as distinctive as possible. Avoid layouts whose local views are visibly indistinguishable.
The Local Imagability Principle - Seek to structure the layout such that adjacent views are predictable from their neighbors.
The Global Imagability Principle - Seek to structure the layout such that local views can be easily situated within a global structure.
The Salient Background Principle - Maximize the visible differences between regions, or the confusions can be worse than not providing regions at all.
The Frequent Feature Principle - Provide explicit features every few views, or navigators may try to invent them anyway.
The Small Divisor Principle - Position and size items in the space to divide its extent into a small number of regularly sized units.
The Alignment Principle - Align landmarks along natural directions of movement to prevent subjects from having to estimate relative direction.
111 Chapter 7 Future Work
This research suggests four broad avenues for future work:
Develop Scalable Design Tools The spaces designed in this thesis were constructed using relatively simple tools of my own design. To support the efficient creation of spaces with many thousands of items, better tools will be required. The ideal design studio would enable a designer to focus on explicitly representing the structure of the data and the activity, not on manually tweaking a layout. To this end, a critical component of a design studio would be a semi-automated tool for laying out a semantic network of items according to a particular presentation method (e.g. 2D, 2.5D, 3D) and a given set of design principles (e.g. space items in small integral multiples to facilitate estimation of relative distance). Another idea would be to implement an agent that could identify potential trouble spots in a given layout (e.g. regions where the mean distance to a landmark is several view lengths) and suggest solutions (e.g. place an explicit feature somewhere in this region).
Develop Scalable Visualization Methods for the LRPDPDElements This thesis has focused on a simple and useful overhead 2D visualization method. However, the design space of presentation styles for landmarks, regions, and paths is quite rich and merits additional investigation. For example, evidence from cognitive mapping suggests that humans build mental models of physical environments at multiple scales [Gollg86]. One idea would be to implement different renderings of each element (e.g. a path) based on the scale of view (e.g. show only the start, end, and branch points at lower resolutions). This research would build towards the general notion of a 'semantic fish-eye view' proposed by Fairchild, Poltrock, and Furnas in their seminal paper [Semnt88]. Extensions of these methods to 2.5D and 3D are natural to consider. Exploring methods to exploit the additional space of 3D without reducing interaction times is of particular interest.
Develop a Taxonomy of Information Spaces Information architecture is still a very young design field. Precedents suggest that collection and analysis of a wide variety of case studies is critical to grounding general principles and eventually a theory. Developing a digital library of design examples and their associated principles would be
112 an invaluable resource for designers. With respect to the spatial metaphor, these examples would help to further refine tests for when and why a spatial metaphor might be a useful approach.
Elaboratethe usability implications of the spatialmetaphor This thesis has centered on the mental model as the key figure of merit in design. Much work needs to be done to further substantiate the models used in navigation and to distinguish the impact of the spatial metaphor. For example, it would be interesting to measure the impact of a spatial metaphor on a purely tree-structured hypertext. Although many popular visualization techniques have focused on trees, I would predict that the performance of a navigator in hypertext would be substantially similar to that of a spatial navigator because a tree has an implicit landmark (i.e. the root) and an implicit direction (i.e. towards the root). As such, the value of a spatial approach may be substantially diminished in tree-structured spaces. The librarian experiment ought to be reproduced in several different spaces to provide more data. In particular, it was clear that individual differences were important and this was most evident in the recall task. Identifying broad categories of navigation styles could enhance navigability by permitting specialization of the space.
113 Appendix A
Experiment Instructions
The Visual Librarian Experiment
This experiment studies how people navigate on the World Wide Web. The experiment has four parts:
1. You will be shown an experimental web browser and given a chance to get comfortable with it 2. You will be ask to perform a series of tasks by browsing a web site 3. You will be given a 10 minute break 4. You will be asked to perform a second series of tasks on the same site
The total time for the experiment will be approximately 90-100 minutes. Are you ready?
Practice P Version This is a small practice world designed to help you get comfortable navigating in a simplified web browser. You may navigate by either following the underlined links [example] or by using the forward and back buttons [example].
Please get comfortable with each of these navigation methods and let me know when you are ready to proceed.
Verification: * Follow the path: apple, eggplant, pizza, and salad * What page would you get to if you pressed the back button twice? Go there. * What page would you go to if you pressed the forward button once? Go there.
Are you comfortable navigating with this interface?
114 SP Version This is a small practice world designed to acquaint you with an experimental web browser. The right panel [point] is a simplified, standard browser. In the left panel, each page on the practice site has been mapped to an item in the landscape labeled with the titles of the corresponding pages [show example].
You may navigate a site in four ways: 1) following the underlined links in the page [show example], 2) by using the forward and back buttons [show example], 3) by moving in the landscape using the arrow and zoom keys [example], or 4) selecting items in the landscape which will automatically navigate your view there [show example]. Notice that the left and right views are synchronized: when you travel from one page to another in one view, the other view updates accordingly.
Please get comfortable with each of these navigation methods and let me know when you are ready to proceed.
Verification: * Follow the path in the right panel: apple, eggplant, pizza, and salad * What page would you get to if you pressed the back button twice? Go there. * What page would you go to if you pressed the forward button once? Go there. * Go to the apple page by selecting it in the left panel. * Center the leftmost white edge in the view, then top, then right, and then bottom * Pan back and center the view on the middle of the site.
Are you comfortable navigating with this interface?
Browsing You will be exploring a web site designed to help people learn about dinosaurs. You will be given 15 minutes to explore the site. Your goal is to learn as much as you can about how the information about dinosaurs has been organized.Imagine that you will be a librarianfor this site: you do not need to memorize every fact, but you ought to know where the answers to questions are located. While you are browsing, talk about where you are in the site, what you are learning about its organization, and why you are making the choices you are making.
115 Please let me know when you are ready to begin.
[Navigate to the home page, zoom out, start timing]
[Test the microphone for distance and volume]. Please describe the organization of the site in as much detail as you can remember. Imagine I am a librarian in training and you are explaining to me how to fmd answers to questions.
Mapping Now I'd like you to use a small program to reproduce as much as you remember about the structure of the site. This is a landscape on which you can add, remove, edit, and link items. [Show examples of each function]. You can navigate in the landscape using the arrow and zoom keys [show example]. You can move items in the landscape by selecting and dragging them [example].
Get comfortable with the program and let me know when you are ready.
Verify: * Please add two items labeled A and B to the landscape * Please change the name of A to C * Please add a link from B to C * Please delete the link * Please delete item B.
Please use this tool to depict as many pages and links between pages as you can remember. Use a single item on the landscape to represent a single page, and use a link on the landscape to represent a hyperlink between pages. You may provide notes on what you saw in the page if you want to, but focus on the page subjects and their relationships rather than the details of any particular page. You will be given 20 minutes. [Please describe any features of the map that might need explanation].
116 WavfLinding I will now read a series of questions; each answer appears on a single page somewhere in the site. Please navigate to the page containing the answer as efficiently as you can. At any time, you may let me know if you feel unable to find the answer, or if 3 or more minutes have expired on one question, I will show you where the answer is and we can continue to the next question.
1. How do scientists estimate how intelligent a dinosaur might have been? 2. How do scientists name dinosaurs? 3. What did Muttaburrasaurus eat? 4. How do scientists estimate the age of a fossil? 5. How did scientists come to believe that T-Rex probably had a very good sense of smell? 6. What was the name of the largest flying animal ever to live? 7. How long did it take for the dinosaurs to go extinct? 8. Why did large dinosaurs probably have high blood pressure? 9. What was the largest carnivoire of the Triassic period? 10. How did dinosaurs communicate? 11. How heavy did Torosaurus get? 12. How long did it take for the dinosaurs to go extinct? 13. What was the first dinosaur fossil found in the United States? 14. Give one piece of evidence that supports the idea that an asteroid killed the dinosaurs 15. Why do scientists believe that dinosaurs are related to birds?
Aperture Experiment Instructions
This experiment will measure your ability to estimate your current visual point of view. The experiment has five steps:
1. You will be shown a small practice world designed to get you comfortable with both the computer interface and the task you will be performing. 2. You will be given a series of trials that will be recorded. 3. You will be given a ten-minute rest period. 4. You will be given another set of trials. 5. You will be asked to answer a short set of questions about how you performed the task.
117 The total time for the experiment will be about one hour. Are you ready to begin?
Practice World The dialog box
Once you hit enter, the viewing window will be automatically shifted to a random location in the landscape
Pressing the 'where am I button?' during the experiment will display a dialog box that shows the current location of the viewing window. The interface will not allow you to press 'where am I' during a trial.
You will now be run through a short practice run designed to acquaint you with the interface and the task you are performing. During the practice, please ask any questions you may have.
Are you comfortable with the interface? Do you understand the task you are being asked to perform?
Questions How did you perform the first task? How did you perform the second task? Did you believe the first set of trials was easier or harder than the second task? Why?
118 Appendix B Maps From the Librarian Experiment
P-Subject Mais
Figure 53 - Map from subject P1
Figure 54 - Map from subject P2
119 ntna
Figure 55 - Map from subject P3
Figure 56- Map from subject P4
120 NEW ---
I
Figure 57 - Map from subject P5
121 Figure 58 - Map from subject P6
I} L
Figure 59 - Map from subject P7
122 Figure 60 - Map from subject P8
Figure 61 - Map from subject P9
123 SP-Subject Maps
-
Figure 62 - Map from subject SP1
124 l - mammon
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Figure 63 - Map from subject SP2
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Figure 64 -Map from subject SP3
125 U- U -.-
M NJ
Figure 65 - Map from subject SP4
126 . i ......
Figure 66 - Map from subject SP5
127 Figure 67 - Map from subject SP6
Figure 68 - Map for subject SP7
128 F 9- rs 7
Figure 69 - Map from subject SP8
129 Fu 7
Figure 70 - Map from subject SP9
130 Bibliography
[AltVa] AltaVista Search Engine; http://www.altavista.com
[Andrs95] Andrews, K.; 'Visualizing Cyberspace: Information Visualization in the Harmony Internet Browser'; in Proc. of IEEE Symposium on Information Visualization; pps: 97-104 (1995)
[BBCDn] The BBC Walking With Dinosaurs Web Site; http://www.bbc.co.uk/dinosaurs
[Cantr85] Canter, D., Rivers, R., and Storrs, G.; 'Characterizing user navigation through complex data structures'; Behaviour and Information Technology 4(2):93-102 (1985)
[CaRbY96] Card, S.; Robertson, G,; York, W; 'The WebBook and the WebForager: An Information Workspace for the World Wide Web'; in Proc. of CHI '96; pps: 111- 117 (1996)
[CarRs87] Carroll, J.M. and Rosson, M.B.; "The paradox of the active user"; In J.M. Carroll (Ed.), Interfacing Thought: Cognitive Aspects of Human-ComputerInteraction; Cambridge, MA: MIT Press.
[Chase8 1] Chase, W. G.; Chi, M. T. H.; "Cognitive skill: Implications for spatial skill in large-scale environments"; in Cognition, SocialBehaviour and the Environment, J. Harvey (ed), Lawrence Erlbaum, Hillsdale/NJ (1981)
[CKPTu92] Cutting, D.; Karger, D.; Pedersen, J.; Tukey, J.; "Scatter/Gather: A cluster-based approach to browsing large document collections"; SIGIR '92
[Cosmo] The Cosmo Player VRML browser; http://www.cai.com/cosmo
[CtSer] The NEC Scientific Literature Digital Library http://citeseer.ni.nec.com
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