Evaluating a Map's Image

Recent psychological evidence suggests that mental images are a functional part of human thought. The mental resources enabling people to deal with image information are of central concern in cartographic communication. This study deals with the goodness of the image information derived from a map display. The term pattern quality describes the quality of an internal image founded upon the apparent form or pattern in the spatial display. Maps can be shown to differ in pattern quality. Four graduated-symbol displays were tested in both unshaded and completely shaded forms. Subjects provided dissimilarity estimates of ten different distributions under two testing conditions. In the first test, pairs of maps were arranged, for comparison, on the same test page (simultaneous viewing). In the second test, maps were placed, for comparison, on successive pages (remembered viewing). Non-metric multidimensional scaling was used to convert the dissimilarity estimates of the ten mapped distributions for every symbol display to a configuration of points in two-dimensional space. Tobler's bidimensional regression was then applied to the two-dimensional configurations. The two-dimensional fit of points for the two viewing conditions yielded information about the pattern quality of the eight symbol displays. The results demonstrated differences in pattern quality among the maps chosen for testing, indicating that the pattern/image information derived from a map can be empirically evaluated.