UNITED NATIONS STATISTICAL COMMISSION CRP.1 and ECONOMIC COMMISSION FOR EUROPE ENGLISH ONLY CONFERENCE OF EUROPEAN STATISTICIANS UNECE Work Session on Communication and Dissemination of Statistics (13-15 May 2009, Warsaw, Poland) Guidelines on the Presentation of Statistical Maps Prepared by Thomas Schulz, Swiss Federal Statistical Office 1. Why use maps? An introduction All numbers that statistics meticulously measure and the findings of its many surveys and censuses do not happen just somewhere, in an empty space. They might take “place” in a specific country, in a region, in a city, in a commune, in a city block, in a building, or at some precise spot on earth – but all of them have one thing in common: a spatial relation, which is stored in statistical databases. Sometimes, this relation is more apparent, while using sophisticated spatial data bases in a geography department. Sometimes, this dimension is but one out of many dimensions in a general publication database. In fact, geography has always played an important role in the collection and dissemination of statistical data. It has even contributed to the emergence of the modern day census. With new technologies for convenient spatial data collection and storage and an increasing awareness of an interested public that uses navigational tools and Internet applications like Google Earth basically every day and at ease, geography has gone beyond scientific inventories and school books. You only need to switch on your T.V. or browse the Internet for election results, weather forecasts or the last aviation accident – geographic location and knowledge are part of our life and thus belong into every statistical publication. Maps and atlases convey geography and describe these spatial relationships. When carefully designed and adequately presented, they are more than just a decorative element in a publication. They serve as valuable decision-making tools for experts, politicians and the general public alike and meet a growing demand in all parts of society. Just as the adage “a picture is worth a thousand words” portrays, it can be stated that “a map is often worth a thousand numbers”. In our visual era, maps can become a very powerful means in the information process and have advantages over other elements of statistical dissemination. 1 The power of maps: 4 elements of statistical publications showing the same topic. Source: Swiss Federal Statistical Office (FSO). Apart from showing spatial patterns and locations (their primary function), which might not be apparent from looking at data tables alone, they are very concise and easy to comprehend. They help to understand an ever growing volume of information – at a glimpse, within seconds of watching it. Maps are a synopsis. They sum up voluminous data from tables. They translate long and complicated textual explanations. And they can integrate dozens of graphs (e.g. pie charts or age pyramids) for single regions or periods into one clear image. During the age of paper publications, maps have often been neglected by statisticians for not portraying exact numbers. This disadvantage has been overcome by modern electronic displays. Nowadays, interactive maps and mapping tools allow everyone to retrieve the actual data “behind the map” by clicking on or passing over tinted areas with a mouse. And multimedia animations have opened every possibility to combine time and space in map time series as well. Characteristics and purposes of map use in statistics Maps can serve various purposes in the preparation of censuses and surveys as well as in analysis and reporting of the results. They can be an inventory and support description, exploration, analysis, confirmation, tabulation or decoration. If at least one of the following applies to your situation, the usage of a map in a publication should be considered: • Maps locate statistical results and give a clear image of the spatial distribution of a phenomenon. Where was the highest temperature recorded last summer? In which county did the Democratic Party get its best results 2008? • Maps enable comparisons and answer multiple questions: between different areas in one map, between different topics in different maps, between variables for the same area in one map or between time periods. Has the population density increased in my district over the last 50 years? Have other districts been affected differently over time? • Maps confirm and validate statistical findings. Is it true that our population is aging, as the report says? • Maps and geographic information systems store spatial knowledge. • Maps support textual and tabular information that are only difficult to explain. • Maps have a synoptic character and summarize large amounts of information. They reduce complexity. It can not be assumed that any reader will ever go through a table 2 with 5000 population data values for a large country like the U.K. or Germany? There is less value in the rows of numbers shown by a table than possibly in one single map. Here, users can easily detect patterns and clusters of high and low concentrations. • Maps convey a concept or an idea. They are a democratic means, easy to understand and can help to better communicate a whole statistical programme and thus contribute to the overall acceptance of for example a population census. • Maps are colourful and have a general positive image. They appeal to the user’s curiosity and attract attention to a publication. They are hung up walls or handed over as gifts in the form of paper or DVD atlases. Situations when not to use a map Nevertheless, there are circumstances when maps should be omitted in publications. This is the case, when there are other favourable solutions that can portray the same information. Or when technical restraints (space, colour, electronic technologies used) hinder the map from communicating properly. Some examples: Not suited for map display: Data only on national level. Source: FSO. • Data is available only for one or a small amount of spatial units. For example, it is not advisable to create a map if the number for the gross domestic product exists only for the whole country, without any regional breakdown. This is, unless one has other country data to compare it with and can put it into an international context. Good example: Graphs for 26 cantons exist and can be converted into a map. Source: Swiss Federal Statistical Office (FSO). 3 • There is no significant variation in the data. When figures for almost all districts show that the death rate last year has only been between 1 and 1.5%, then it is fairly stable all over the country. Specific spatial patterns for analysis will not be found. • The user groups have not been defined or it can not be assumed that potential users understand maps or graphs easily. Sometimes also accessibility (esp. for visually impaired persons) can be a reason to do without maps. • The publication will only appear in black & white. Maps do only unfold their real power once they can use colours. We live in a digital age, and this should apparently no longer be a problem for Internet and electronic dissemination. Surprisingly, even on the Internet, many black & white maps can be found. • There is not enough space in a publication. Maps portray space and they do need space themselves. Containing a hundred regions or more, they can take up to half a page in an A4 publication. If you have only a few centimetres left at the bottom of a page or 200 pixels in width on your web page, then maps should not be integrated. Bad example – where a map is not the best solution: Proportion of native Hawaiian and other Pacific Islanders in the total population of the United States (map below). Not even 10% of the counties contain detectable information. 90% of the map is virtually empty. Apart from one single county (green), all other areas belong in one class (0.1 – 0.9%) and can not be differentiated visually. Solutions: use a table for the few counties or a regional map for the Western part of the Unites States. Source: U.S. Census Bureau, Mapping Census 2000. 4 2. Maps and Atlases A short functional classification Maps are one of the oldest means of communication. Over time, a large variety of different styles and methods have been developed by cartographers and other scientist. They can be classified according to scale, function, design, production technology, or the way they are used in a publication. In general, there exist two functional types of maps: • General reference (topographic) maps : support orientation in space and show locations of a variety of different features, such as water bodies, mountains, coastlines, roads. They help readers to detect the boundaries of specific geographic areas, such as provinces, cities, counties or health regions. • Thematic (statistical) maps : are used to show the spatial distribution of one or more geographic attributes. A thematic map is always designed to serve some purpose and answer specific questions. Readers can view all imaginable data themes in thematic maps such as political, social, cultural, economic, agricultural or natural phenomena that exist on the earth’s surface or even below or above in space (e.g. lunar maps). General reference maps are used in statistics only for the preparation of censuses or the attribution of data – whenever something has to be oriented in space. Parts of their content are also used as base information for thematic maps. Maps that display statistical data are more relevant for publications and called thematic maps . In fact, statistics and censuses have largely stimulated the development of new methods in thematic mapping. The terms statistical and thematic maps can be used almost synonymously. It is estimated that 85% of the existing maps are thematic maps.