The Science and Art of Designing Good Maps

By Professor Chinmaya S Rathore

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Figure 1: An Antique map of Lancashire railways
showing north arrow, scale bar, coordinate grid,
neat line,drop shadow and pictorial transport marginalia.

A lot of people these days are using Geographic Information Systems (GIS) for environmental and natural resource problem solving. The end results of most such geographic analyses (which mostly rely on maps created by others) need to be communicated through maps that the GIS analyst needs to design and produce themselves. Designing good maps that can effectively and accurately communicate information however is a difficult task falling in the realm of a subject called Cartography which is unfortunately not extensively taught or emphasized in many GIS courses. The result is that many maps resulting from such GIS analyses, suffer from serious design flaws due to lack of cartographic insights and best practices. Monmonier (1996) refers to such map design transgressions as an ‘cartographic insult’.

While it is not the intent of this post to serve as a primer in digital cartography, it makes a modest attempt to point the   reader to some excellent resources and tools that can help quickly build a better understanding of key map design principles to create better maps. This post particularly focuses on the appropriate use of colour, an element that is most commonly used in maps but arguably, the most abused.  

Cartography is the making and study of maps in all their aspects (Robinson et. al 1995). Buckley (2012) shortlists five key cartographic principles that the map maker needs to keep in mind to design good maps. These are (1) Visual Contrast (2) Legibility (3) Figure-ground Organization (4) Hierarchical Organization and (5) Balance. Visual contrast essentially refers to the contrast created by the choice of colors or gray scales that can make map features, other page elements and map background stand apart. Legibility defines whether map elements can be properly seen and consequentially understood. Making the judicious decisions in choosing appropriate symbols, fonts and suitably sizing them results in legible maps. Figure-ground organization refers to the natural separation of the overall map figure from the background. Hierarchical organization denotes visual layering of map elements in a manner that essentially brings important map content to the fore. In other words, through suitable hierarchical organization, the map maker ensures that the main message that the map requires to convey remains firmly in the foreground. Finally, balance, like a Zen garden, is about arranging and organizing map elements in a manner that brings equilibrium and harmony to the map. Highlighting the importance of these principles Aileen Buckley points out the following:

"Visual contrast and legibility provide the basis for seeing the contents on the map. Figure-ground organization, hierarchical organization, and balance lead the map reader through the contents to determine the importance of things and ultimately find patterns."

Interested readers are encouraged to peruse Aileen Buckley’s Excellent article for more details and some great pictorial examples that visually illustrate each of these five design principles. The British Ordinance Survey expands this list of design principles and provides an excellent resource on cartographic design principles with real examples explaining each principle. Readers might also like to visit the Geographer's Craft website developed by the Department of Geography, University of Colorado at Boulder for a short course on cartographic communication. 

Having briefly discussed key cartographic principles, lets now focus on color which is abundantly used to depict and differentiate various features and elements on GIS generated maps. While color is the primary vehicle to enhance visual appeal and introduce visual contrast on the map (design principle 1 above), its appropriate choice is often a complex decision even for the experienced map maker. Monmonier (1996) sums up the situation in the following words:

“Color is a cartographic quagmire. The complexity and seductiveness of color overwhelm many mapmakers, and countless maps in computer graphics demonstrations, business presentations and daily newspapers reveal a widespread ignorance of how color can help or hurt a map. Persons unaware of the appropriate use of color in cartography are easily impressed and might accept as useful a poor map that merely looks pretty. Colors decorative role easily conflicts with its functional role.”

Before proceeding further, a brief description of the color theory is in order. For cartographic purposes, color is best described on three dimensions - Hue, Saturation (Chroma) and Value (the HSV or HSB color-space) – by the Munsell Color System (Figure 2). In simple words, hue which is represented as the circle in Figure 1 is another name for color, the dominant wavelength like violet, indigo, blue, green, yellow, orange, red. When you speak the name of a color, you are in fact referring to its hue. Saturation or Chroma, shown on the scale radiating outwards in Figure 2, refers to the intensity or purity or brilliance of that color. Value, which is represented as the central pillar in Figure 2, is the amount of black (produces shades) or white (produces tints) or gray (produces tones) mixed with a hue or color. In Figure 1 below for example, the hue is Purple-Blue, the value is 5 (the amount of gray mixed with the hue) and 0 – 12 on the outward radiating scale is the saturation with 12 indicating 100% brilliance or intensity (a vivid fully saturated purple blue) and 0 reprinting compete desaturation of the hue to the base gray color. An excellent expansive discussion on this subject can be Leigh Cotnoirs learn site. 

 Figure 2: The Munsell Color System

The reason why the choice of the correct colors for maps is complicated and confusing is because colors can be used on a map to show differences in kind, differences in intensity, to make features attractive or unattractive and also because color preferences can vary significantly due to factors such as culture, life cycle and demographic characteristics (Monmonier,1996). Wrong choice of color to depict certain features can also create considerable confusion in the minds of map users conditioned to culturally interpret a particular color in a certain way. In summary therefore, the ignorance of color can significantly devalue or complicate the message that the map maker intends to convey.

So is there an easy way out for the ‘in-a-hurry’ GIS analyst from the ‘color quagmire’? Yes, thanks to Professor Cynthia Brewer of Penn State University and an outstanding free online tool developed by her called the Color Brewer 2.0 .

Figure 3: Color Brewer 2.0 landing page

The color brewer shown in Figure 3, provides exactly what it says – color advise for cartography. In the right pane marked 1 in Figure 3, a specially designed map is displayed which acts as a diagnostic tool. The lower left corner of the map is a random section of polygons belonging to the number of data classes you have chosen via drop down (2). This section has polygons of all classes such that the map maker can assess if sufficient contrast exists between them to discern each class individually. The map just above the random section shows chosen classes in preset single or multi hues as chosen using the color picker (4). Notice in figure 2 above, that each class has one polygon each of the other remaining classes for the map maker to facilitate assessment of contrast between classes if surrounded by a dominant class. Click on the ‘how to use’ link encircled by the yellow rectangle in Figure 3 to seek answers to 2 tests to determine if you have hit the right color combination for your map.

Using the checkboxes in the context section (6), you can overlay roads, borders and city labels to further visualize how your chosen color scheme matches up to these elements. Using the background section (7), you can add a terrain backdrop in case you are planning to overlay your map features over terrain. You can finally note Hex or RGB color codes (9) and use them to recreate the color scheme in your chosen GIS environment. The highlight of this tool which makes it stand out in offering color advise for cartography is the selection options for nature of your data (3). The icons shown encircled in blue provide great background information on what various choices in a section mean. Screen sections 5 and 8 are self-explanatory and you can try them out to see their effect. In summary, Color Brewer is a great tool that GIS map makers should access very frequently in order to quickly create high quality maps.

Another great resource for map color gradients that I wish to point to the reader is the cpt-city site created and maintained by Dr. J.J. Green.  This fantastic archive not only hosts a sizeable collection of color gradients and sample map miniatures, it also permits you to download these ramps in many different formats.

In conclusion, this post has tried to highlight the importance of being aware of cartographic best practices while designing and creating maps resulting from GIS analyses. While the discussion presented in this post is no substitute to comprehensive training in cartography, it makes an attempt to serve as a launch pad to lure the reader into the fascinating world of cartographic design. The celebrated British film director Peter Greenway sums this quest beautifully:

“I’ve always been fascinated by maps and cartography. A map tells you where you’ve been, where you are, and where you’re going — in a sense it’s three tenses in one.”

😊

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Literature Cited

Buckley, A. 2012 Make Maps People Want to Look At, ArcUser Winter 2012, ESRI.

Monmonier M. 1996 How to Lie with Maps, 2^nd Edition Chicago: University of Chicago Press

Robinson, A.H, J.L. Morrison, P.C. Muehrcke, A. J. Kimerling, S.C. Guptill. 1995 Elements of Cartography, 6th Edition, New York, Wiely