A Case for Better Graphics: The Unclassed Choropleth Map

In recent years a number of researchers have shown a strong interest in statistical graphics. One widely used graphical method is the “statistical map,” or what is better known in cartography as the choropleth map. A factor in the use of these maps has been the need to group data into classes, raising the obvious question of defining optimum class intervals. Computer technology now makes it possible to produce unclassed choropleth maps, minimizing quantization error. An example of the two methods is given using criminal justice statistics. The unclassed maps are more accurate with regard to quantization error and appear to be of superior visual quality