Geographical Information Systems (GIS) are databases with powerful mapping capabilities and, for this reason among others, they are becoming increasingly associated with environmental studies of all kinds, including EIA. The definition of GIS has been the subject of some debate (Maguire 1991), and although GIS can be simply described as databases where the information is spatially referenced, what has made GIS so popular is the fact that the spatial referencing of information is related to “maps”. It is the manipulation and analysis of the spatial database and the display of maps with relative speed and ease that is the trademark of GIS.