Miscommunicating With Isolines: Design Principles for Thematic Maps

M. Violet Gray RBF Consulting Camarillo, California [email protected] Gould and White (1968) introduced the measurement and isoline mapping of regional preferences, producing preference or “isoeutope” maps. As cartographers know, the decision to employ isoline mapping as a cartographic display technique is valid insofar as certain assumptions are met, notably the assumption that the variable being mapped reflects an underlying continuum. This assumption is doubtful in the case of a variable such as regional preference insofar as it is based on rankings or ratings of existing regional units such as states for which human cognition is not continuous. The implications of mapping preference with isolines are discussed, particularly with respect to the attitudes they reflect and the cognitive responses they elicit in viewers. We argue that isoline mapping of data such as state preferences produces misleading impressions of intraregional variation and is neither necessary nor desirable. Alternative methods for the collection and cartographic display of regional preference data are discussed. Notably, we propose the use of “psuedo-Chernoff” faces as an appropriate technique.