Systems that allow users to store and retrieve spatial data, provide for analyses of spatial data, and offer highly
detailed display of spatial data are referred to as geographic information systems, or more typically, GIS. Since
their initial usage in the 1960s, GISs have evolved as a means of assembling and analyzing diverse data
pertaining to specific geographical areas, with spatial locations of the data serving as the organizational basis
for the information systems. The structure of GISs is built around spatial identifiers and the methods used to
encode data for storage and manipulation. This paper examines how GIS has been used in typical
environmental assessment, its use for cumulative impact assessment, and explores litigation that occurred in
the United States Federal court system where GIS was used in some aspect of cumulative effects. The paper
also summarizes fifteen case studies that range from area wide transportation planning to wildlife and habitat
impacts, and draws together a few lessons learned from this review of literature and litigation.