Color in Map Design

One of the principal methods of communicating geographic information is visually on a map. For both two-dimensional paper maps and digital maps displayed on a computer screen, color is often an essential component. The use of color in map design is a method of symbolization where hues, sometimes with varying amounts of saturation and intensity, are employed to symbolize features and differentiate between values for quantitative and qualitative spatial data. A hue is a distinct wavelength of visible light. The purest hues include blue, green, and red. Saturation refers to the amount of color, or hue, displayed on a surface area, and the intensity of color is associated with the brightness of hues. When applied properly, the use of color in maps enables more effective communication of spatial information. Used improperly, color will not only decrease the effectiveness of communication but can also lead to false interpretations of the information. An awareness of the intricacies of color use in map design and the incorporation of common cartographic conventions developed to address some of those intricacies will promote more effective communication of spatial information in maps.

Color can be used in both raster and vector data to represent a range of values within cells or to give more meaning to point, line, and area features. There are many considerations when using color in map design that collectively make the process of choosing appropriate colors intricate. For example, color provides an additional amount of contrast to map symbols that can add weight to the meaning and/or values of features on a map. In addition, certain colors have connotative and associative meanings. Moreover, interpretation of the meaning may vary for different map users. Thus, a brief discussion of these and other considerations is in order. Some considerations include color connotation and psychological reactions, color association, color interactions, and light source.

Different colors and variations in color intensity may have a variety of connotations. For example, when viewing a map of voting results by county within California for a proposition, counties could be symbolized with color to represent those that voted in favor of the proposition versus those that voted against. If we chose red to symbolize those in favor and blue to symbolize those that voted against, both colors are the same level of purity and the same intensity and saturation. Consequently, one color does not stand out over another. Thus, these colors provide equal weight and importance to each result. In addition, the colors are clearly distinct. A connotation that might result from the use of red and blue is in the relation of these colors to the Republican and Democratic parties, respectively. The use of blue for those counties that voted in favor might imply that the decision is also supported by the Democratic Party. If, [Page 519]however, we chose red for those in favor and yellow, a less pure color resulting from the combination of red and green, for those against, the red counties would stand out more on the map and potentially harbor a connotation that the decision to vote in favor of the proposition is more important than the decision to vote against. When a hue is used with different saturation levels and or intensities to create a range of color for symbolizing features on a map, lower saturation and intensity levels might be interpreted as having less value than those categories that are represented with higher saturation and intensity levels. This might provide clarity when representing quantitative data in a map of precipitation. However, when used with qualitative data, such as a map of dominant ethnicity, the use of those same colors might imply that there is an order to the data that does not exist.

...