6-5 Color Map

Visualization using color is now available with color monitor or color printer connected to a computer. However to select color codes of R, G, B for color output is not easy to produce a beautiful and meaningful color image.

The objective of color map is categorized into the following two types.

Representation of similarity
There are two types;

1. Numerical values of all positive or all negative in a certain order. Elevation or ground height on the land is usually all positive. Water depth is all negative. Such values will be represented continuously by similar color codes, particularly by intensity or brightness.

2. Numerical values with plus and minus or over and under the average. Temperature is an example. Red color will be used for higher values while blue color for lower values. The average will be yellow or green color.

Representation of separability

Different color codes will be better used to enhance the difference of attributes, for example land use, soil, geology, vegetation etc. To select more than twenty colors would be so difficult to identify the color difference on the color image. About ten colors would be recommendable.

Because in GIS many letters and lines will be added on the color map, the brightness of color should be rather high. In most case, different hues with almost equal intensity and saturation would be a better color combination on the color map.

Table 6.4 shows R, G, B color codes of three color pallets for similarity and two color pallets for separability visualizations.

The color samples are shown in the front page of this book.