The Role of Complexity and Symbolization Method in Thematic Map Effectiveness

Thematic map effectiveness can be defined only in terms of specific user requirements. Consideration of common requirements results in four criteria by which map effectiveness is evaluated: effectiveness for direct acquisition of both specific and general information and for memory of both specific and general information. The influence of visual map complexity and two methods of symbolization (choropleth and shaded isopleth maps) on each aspect of complexity is evaluated. Though isopleth maps prove to be consistently less complex than choropleth maps, the only significant difference in effectiveness between the methods is for memory of general patterns, in which case isopleth maps are more effective. Map complexity is found to have two components that influence effectiveness in quite different ways. Complexity of a mapped distribution is inversely related to effectiveness of maps in communicating general patterns but has little relation to communication of specific details. The second aspect of complexity, the number of classes, is inversely related to communication of specific details but exhibits little relationship to communication of general patterns.