Color sequences for univariate maps: theory, experiments and principles

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Abstract
Pseudocoloring for presenting univariate map information on a graphic display system is investigated. The kinds of information available in maps are divided into two classes: metric information denotes the quantity stored at each point on the surface, and form information denotes the shape or structure of the surface. Theoretical principles are proposed to predict which color sequences will be effective at conveying value and form information respectively. According to this theory, a scale that approximates the physical spectrum should be good at conveying value information, because of the reduced effects of simultaneous contrast. It should be poor at conveying form information, however, because the brain prefers form information to come through the lightness-processing channel. Conversely, a gray scale should be poor at conveying value information and good at conveying form information, according to the same theory. These predictions are tested in a series of psychophysical experiments that test five color sequences. The results show that simultaneous contrast can be a major source of error when reading maps, but only partially confirm the form hypothesis. Guidelines are given for designing color sequences to be effective in both conveying form and value information. An experimental color sequence is presented to illustrate these guidelines.