Cartographic design and the quality of climate change maps

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224 Climatic Change (2009) 95:219–230 appropriate color schemes is determined by whether the attributes are qualitative (use different colors to symbolize different ecotypes) or quantitative (use the same color with variation from light to dark to symbolize changes in temperature over time). Cartographic principles guide decisions about how to group (‘classify’) data for representation. For example, a map showing temperature ranges may have temperature data assigned to groups using equal intervals (same data range for each class) or quantiles (same number of data points in each class). Cartographic principles guide decisions about how to arrange all the graphic symbols included on a map so that there is clarity in the overall design and layout. Numerous texts review and explain cartographic principles (see, for example, Slocum et al. 2005; Kimerling et al. 2001; Dent1999; Robinson et al. 1995; MacEachren1994; Monmonier 1993). There is strong consensus within the cartographic community about basic principles. Contemporary map design also demands understanding the constraints and opportunities determined by the media on which a map will be reproduced. For example, maps designed for digital display are limited by screen resolution compared with maps designed for printing on paper, and ‘endless zoom’ options carry with them unique problems of data accuracy and cartographic design (see Lobben and Patton 2003, for a comparison of design issues for digital and printed maps). Table 2 Selected introductory resources on cartographic design Books (full citations are listed under references) Cynthia Brewer, Designing Better Maps: A Guide for GIS Users Borden Dent, Cartography: Thematic Map Design, 5th edition Jon Kimerling, Philip Muehrcke, and Juliana Muehrcke, Map Use: Reading, Analysis, and Interpretation, 5th edition John Krygier and Denis Wood, Making Maps: A Visual Guide to Map Design for GIS Alan MacEachren, Some Truth with Maps: A Primer on Symbolization and Design Mark Monmonier, How to Lie with Maps, 2nd edition Terry Slocum, Robert McMaster, Fritz Kessler, and Hugh Howard, Thematic Cartography and Geographic Visualization, 2nd edition Journals Cartographic Perspectives (Journal of the North American Cartographic Information Society; http://www.nacis.org) Cartography and Geographic Information Science (Journal of the Cartography and Geographic Information Society; http://www.cartogis.org) Cartographica (Journal of the Canadian Cartographic Association; http://www.cca-acc.org/) The Cartographic Journal (Journal of the British Cartographic Society; http://www.cartography.org.uk/) Websites http://www.colorbrewer.org (an interactive online tool designed to assist in selecting good color schemes for maps and other graphics) http://www.typebrewer.org/ (an online tool designed for people who want to learn more about map typography) http://www.progonos.com/furuti/MapProj/Normal/CartProp/cartProp.html (an introduction to map projections, with examples of distortions, and a discussion of matching projection to a map’s purpose) http://mappingcenter.esri.com/ (a website that focuses on cartographic resources, examples, and assistance for users of ArcGIS)
Climatic Change (2009) 95:219–230 225 Table 1 includes selected cartographic principles adapted from two recent books that focus on map design (Brewer 2005; Krygier and Wood 2005). Specifically, Table 1 describes principles concerning map projections, generalization, data classification, map layout, visual variables (such as color), visual hierarchy (important information is visually prominent in the map’s design), and more. The sources were selected because their focus is on teaching GIS users how to make better maps, and can introduce non-cartographers to the basics of good map design. The list of principles, though not exhaustive, deals with common design issues encountered in mapping. For example, all maps displayed in two dimensions require mathematical transformation of spherical coordinates to plane coordinates through the use of a map projection. All map projections have distortions of distance, area, direction, and/or shape. Such distortions are particularly noticeable on small-scale maps, such as maps of the world. A map projection that preserves relative areas should be used for maps showing data distributions. While these principles are basic and straightforward, their application in the overall design and layout of a map is often complex and challenging, can involve design tradeoffs, and is a requirement for high quality map design. For climate change scientists interested in learning more about cartographic design, Table 2 provides a list of selected resources that include numerous examples of good and poor map design. 4 Evaluating the IPCC climate change map: an example approach Figure 1 from the IPCC Working Group II summary report for policymakers can be evaluated using the selected principles in Table 1. Each principle can be systematically applied to the map with the result rated as good, satisfactory, orpoor followed by a brief explanation. We applied this method to the IPCC map shown in Fig. 1. Table 3 includes the rating of the map for each selected principle with its explanation. Our preliminary and limited evaluation indicates that the map published in the summary report of Working Group II for policymakers ranges from poor to satisfactory in its use of selected cartographic principles. For example, we rated map layout and focus as poor. The map legend is complex and includes data not even displayed on the map, i.e., the number and percentage of significant changes in the series of four-celled tables with arrows. The legend is also the same size as the map, and they visually compete with each other for importance on the page. Information about the white areas on the map is included in the caption but not in the map legend. Meaningful relationships between changes in physical and biological systems and changes in surface temperature are difficult to see. We rated the generalization of features on the map as satisfactory. The map shows coastlines and boundaries between nations. The black linework to symbolize coastlines and boundaries is more detailed than needed for the scale of this map. The high level of detail for the southern tip of Chile means that the black boundaries blend in with the point locations (blue circles with black outlines). Table 3 summarizes results for each of the selected cartographic principles. Overall, our evaluation is that the map does not clearly and effectively display information about its intended topic, “changes in physical and biological systems and
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Cartographic design and the quality of climate change maps

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