Numbers of Classes and Choropleth Pattern Characteristics

Choroplethic map patterns are affected by the number of class intervals on the map. Four mathematically-defined pattern attributes—map blackness, aggregation, complexity, and contrast—are here compared when differing numbers of intervals are used to represent 17 different geographic variables using the Jenks-Caspall classing procedure. Analysis of the map series shows that: (1) the attributes are significantly affected by the number of classes but at a decreasing rate as the number of classes increases; (2) pattern variability among maps of different distributions decreases with increasing numbers of classes. These findings substantiate the contradictory relationship between map enhancement and map consistency. Few classes provide emphasis or enhancement of map pattern, but a four-class map, for example, may be quite different than a three-class map of the same distribution. Many classes result in a more stable representation of the specific distribution, but the characteristics of the map also differ less from those of maps representing other distributions.