Communication Aspects of Value-by-Area Cartograms

The value-by-area cartogram is a form of mapping often used for its visual impact. The average reaction to cartogram area is potentially error free in that the components of a typical value-by-area cartogram are areal shapes. When not in map form, map readers generally respond to these areas in a linear fashion. Results of a testing program to measure this ability suggest that the accuracy of the average response depends upon whether shapes are amorphous or square and whether the anchor stimulus is relatively large or small. The accuracy of responses to the cartogram compare favorably with responses to a five-class Flannery circle map. Map reader attitudes point out that these cartograms are thought to be confusing and difficult to read. At the same time they appear interesting, generalized, innovative, unusual, and having—as opposed to lacking—style. Communication depends on how well the cartographer has maintained the overall shape quality of the original geographical units and the provision of an adequate stimulus anchor, a geographical-base inset map, and labeling on the statistical units.