Geographic information systems (GIS) have taken on an increasingly important role supporting organizational decision making. The effectiveness of GIS as a decision support tool comes primarily from the visual display of data in the form of maps. When presenting information as a geographic map, the level of data aggregation used potentially affects aspects of task complexity such as information load and the potential for pattern recognition by the user. Other task attributes related to data aggregation effects include problem size, data dispersion, and users’ spatial orientation skills. Results from an experiment indicate that all of these map information characteristics have significant influence on decision performance.