How Information Visualization Novices Construct Visualizations
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How Information Visualization Novices Construct Visualizations Lars Grammel, Melanie Tory, and Margaret-Anne Storey Abstract —It remains challenging for information visualization novices to rapidly construct visualizations during exploratory data analysis. We conducted an exploratory laboratory study in which information visualization novices explored fictitious sales data by communicating visualization specifications to a human mediator, who rapidly constructed the visualizations using commercial visualization software. We found that three activities were central to the iterative visualization construction process: data attribute selection, visual template selection, and visual mapping specification. The major barriers faced by the participants were translating questions into data attributes, designing visual mappings, and interpreting the visualizations. Partial specification was common, and the participants used simple heuristics and preferred visualizations they were already familiar with, such as bar, line and pie charts. From our observations, we derived abstract models that describe barriers in the data exploration process and uncovered how information visualization novices think about visualization specifications. Our findings support the need for tools that suggest potential visualizations and support iterative refinement, that provide explanations and help with learning, and that are tightly integrated into tool support for the overall visual analytics process. Index Terms —Empirical study, visualization, visualization construction, visual analytics, visual mapping, novices. 1 INTRODUCTION Information visualization (InfoVis) is becoming a mainstream visualization construction, which common patterns appear, and technology that is being utilized by InfoVis novices – those who are which barriers and problems InfoVis novices encounter. not familiar with information visualization and visual data analysis. Our work makes three primary contributions: first, we empirically Sites such as Many Eyes [37] enable anyone to upload and visualize examine how information visualization novices construct data, and systems that fall under the umbrella of casual InfoVis visualizations; second, we derive abstract models describing barriers provide visualizations in everyday life [30]. Despite this progress, in the data exploration process and how information visualization the vision of InfoVis for and by the masses has not yet been realized novices think about visualization specifications, and finally, we [14, 17]. Part of the reason for this is that constructing perceptually provide implications for tool design based on our findings and effective visualizations, and even interpreting moderately complex models. ones, remains challenging for InfoVis novices. Interacting with visualizations has become easier with recent tools such as Many Eyes, Tableau etc. However, many potential users that 2 RELATED WORK could benefit from these tools lack visualization construction There are several models of information visualization processes that expertise. In particular, it has been noted that users have difficulties describe the different steps users follow in configuring and using deciding how to map data elements to graphic attributes [14]. This is visualizations to gain insights. Card et al.’s reference model for especially problematic because selecting inappropriate visual visualization ([3], see Fig.1) describes how visualizations are mappings can impede analysis and even result in misleading created in four steps and how the user interprets and interacts with conclusions. It is therefore important to provide tool support that visualizations. First, raw data are processed and transformed into enables InfoVis novices to design good visual mappings easily [14]. data tables (data transformations ). Data tables can be further To create such tool support, we need to understand how InfoVis transformed, for example by filtering, adding calculations, and novices think about and express visual mappings, which barriers they merging tables. The resulting data tables are then mapped to visual encounter, and how this impacts the sensemaking process. Once the structures (visual mappings ), which are generic visual representation specific characteristics of visual mapping expression are uncovered, mechanisms such as line charts or maps with their corresponding we can build tools that specifically support this process, for example visual properties. After the data tables are mapped to visual by reducing discovered barriers. Such tools could potentially enable structures, views of the visual structures can be rendered and a larger audience to leverage visual data exploration and analysis for displayed to the user. Different views show different parts of the decision-making and insight generation, both in work and in daily visual structures at varying levels of abstraction from different life. perspectives. View transformations are operations that change those While general models of the visualization process have been views, e.g. zooming on a map can change the visible part of the map proposed (e.g. [3, 5, 35, 38]), it remains unclear how these models and the level of detail, but does not change the visual structure. The apply to visualization construction by InfoVis novices, and exactly user interprets the views with a task in mind, and can interact with how a lack of visualization expertise impacts sensemaking. To the visualization by changing data transformations, visual mappings explore this in detail, we designed an exploratory laboratory study and the current view. that investigated which processes novices typically follow during Chi’s Data State Model [6] extends and formalizes Card’s reference model by allowing for multiple pipelines, and by having nodes represent state and directed edges represent single • Lars Grammel is with the University of Victoria, transformations operations. Chi also analyzed different visualization E-Mail: [email protected]. techniques and showed how they fit into the Data State Model [5]. • Melanie Tory is with the University of Victoria, E-Mail: [email protected]. Spence [35] identified selection, encoding, and presentation as the • Margaret-Anne Storey is with the University of Victoria, main steps in the transformation from raw data to visualization. Ware E-Mail: [email protected]. [38] devised a model of the visualization process that explicitly takes data gathering into account, but does not distinguish between data Manuscript received 31 March 2010; accepted 1 August 2010 ; posted online tables, visual structures, and views. Ware’s model contains four 24 October 2010; mailed on 16 October 2010. stages: collection and storage of data, data pre-processing, For information on obtaining reprints of this article, please send construction of image, and the human perceptual and cognitive email to: [email protected]. system. Table 1. Participants. Data Analysis (DA) performed Daily (D), Weekly (W), Monthly (M), Never (N). #VCCS indicates number of visualization construction cycles created by participant (see Section 3.7). Participant ID 1 2 3 4 5 6 7 8 9 Age 22 22 21 23 20 21 24 20 21 Fig.1. Visualization Reference Model by Card et al. [3]. The aspects Gender M F F F F F M F F that were investigated in this study are emphasized. DA D D W M M N W N W Several aspects of these visualization models, such as view interaction (e.g. [19, 34, 40]), individual analytical processes (e.g. # VCCs 13 11 18 18 22 13 29 18 8 [1, 12, 29]), and team level analytics (e.g. [16, 32]), have been dynamic, we argue that elements of the process will be the same, and explored in depth, but an understanding of how users construct visual that by introducing communication with a mediator, we achieved mappings remains limited. Several case studies present how deeper insight into how users think about visualizations, similar to a visualizations are created from a designer’s point of view [31] or as a think-aloud protocol. close interaction between designers and users [39]. These studies found that an iterative process of prototyping visualizations is 3.1 Pilot Studies essential: detours are often unavoidable and can provide valuable knowledge. While these studies provide insights into the The study design was shaped in a series of five pilot studies with visualization construction process, they assume experts create the four participants – the same person participated in the first two visualizations for users, whereas our study focused on how InfoVis pilots. In the first pilot, the participant directly used Tableau Desktop novices create visualizations for their own use. This shifts the focus 4.1. It turned out that the user interface and instructions influenced from facilitating communication and iterative domain understanding the participants’ behaviour, and we could not determine whether to bridging gaps caused by a lack of visualization expertise. Heer et problems occurred because of the interface or lack of understanding al. [14] devised some guidelines on how to support novice users: of how to create visual mappings. After the first pilot, we switched facilitate user-friendly data input, provide automatic selection of to an approach where the participants told a human mediator how visualization type using sensible defaults, and provide contextual they wanted the data to be visualized, and the mediator in turn information that explains which data are displayed and which created the visualizations for the participants. In contrast to Wizard-