Guidelines for the Display of Attribute Certainty

This research investigates how the inclusion of attribute certainty in map displays influences GIS modeling and spatial decision support. The goal is to establish empirical evidence documenting graphical guidelines that can be incorporated as GIS system defaults for mapping attribute certainty. Value, texture, and saturation appear as visual variables associated with the depiction of attribute certainty. These three variables, in addition to the level of map detail, are explored in this research. A hypermedia document has been developed to simulate decision makers' use of certainty information for two locational siting tasks: the siting of a park and the siting of an airport. The experiment has been designed to observe the correctness, time, and confidence of both siting decisions. The experiment further determines how variations in symbolizing attribute certainty (by value, saturation, or texture) affect the three variables of correctness, time, and confidence. A third goal focuses on whether the difficulty of the task affects the decision. On a theoretical level, this research uncovers new information about assimilating data quality information into spatial decision support. On a practical level, it establishes symbolization schemes for representing attribute certainty on thematic maps. These should be incorporated as GIS graphical defaults in anticipation of digital data sets that include data quality information. This research is a continuation of a long-standing tradition of empirical research in map design as a paradigm for eliciting and formalizing cartographic knowledge.