An Evaluation of Unclassed Crossed-Line Choropleth Mapping

In Tobler's unclassed mapping, the computer is used to create a virtually continuous array of crossed-line shadings from white to black, thus eliminating the need to generalize quantitative area distributions into classes. Criticism of this method has centered on potential interpretation difficulties for the map user. These and other issues have been examined through subject testing. A preliminary test concerning the relationship between calculated and perceived values for crossed-line shadings showed that people tend to underestimate value differences and an exponent was derived to compensate for this underestimation. A comparative evaluation between unclassed and traditional class-interval methods of choropleth mapping based on critical attributes of choropleth map communication indicate that judgments of both relative and absolute values for individual areas are improved with the unclassed method while there is little difference in the quality of the overall pattern produced by the two methods, at leas...