7.4 What Kinds of Colors Are Best to Use with GIS Maps?

The choice of colors for a map is also important—first to create something pleasing for the map reader, but also in terms of graphic design and usability in a digital format. For instance, the choropleth maps in Figure 7.8 use a range of values of dark green for low percentages and dark blue for high percentages, but there are a lot of ways those classifications could have been colored. There are different color schemes for use in GIS maps—one of these is RGB, a setup used for design on computer screens. RGB utilizes the colors red, green, and blue as the primary colors, mixing them together as needed to create other hues. Another is CMYK, used in graphic design, which uses the colors of cyan, magenta, yellow, and black (the “K” of the acronym) for creating hues. Chapter 10 will deal further with generating different colors from an initial set of primary colors in the context of examining digital imagery.

With a reference map, different colors are used to represent the various objects and symbols. On a choropleth map (like those shown in Figure 7.8), a range of colors is needed to show the lowest classes of data through the highest classes. In this case, a color ramp is used to show a set of colors to represent the classes of values. A color ramp is a selected set of colors that will show the different color changes of a color scheme—for instance, using a single hue of a color in a color ramp might run the range of lightest to darkest blue or light green to very dark green. Other color ramps (like those shown in Figure 7.8) incorporate multiple hues ranging from green through blue. Several different examples of color ramps are shown in Figure 7.9.

Part of why color choice becomes important with a map is the wide range of visualization media that are available for viewing it. Colors of map items may appear one way on a computer monitor, another way when they’re projected onto a screen with an LCD projector, and appear differently yet again when they’re printed on an inkjet or laserjet printer. Just because you like the look of the shades of blue and green on the GIS map on your monitor, you shouldn’t assume that the same colors will translate the same way to a printed page, or to a photocopy of the printout. Your colors might easily have a “washed out” appearance when the map is projected onto a big screen. Check out Hands-on Application 7.5: ColorBrewer Online to investigate the effect that different color choices will have on a final map.