Perceptions of Variable Similarity on Bivariate Choroplethic Maps

The major function of a two-variable map is to depict the spatial variation in the relationship between the two variables mapped. This research studies the methods by which map readers interpret this relationship within each choropleth zone. Using two different map designs, the United States Bureau of the Census colour-coded map, and the continuous tone map, subjects were to form regions of contiguous zones based on perceived relationships between the variables. Both map reading groups performed the task satisfactorily; their methods of solution were similar, and the regions selected were very similar. Each map design produced reasonable results, and each showed some limitations.