ABSTRACT
During the last twenty years the handling of geographic information has undergone a major change due to the rapid emergence of geographical information systems. A geographical information system (GIS) can be conveniently defined as a software package for the storage, analysis and presentation of geographical information. A GIS thus provides the user with a set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes (Burrough, 1986). GISs have quickly become an indispensable tool for efficient management of spatial data and are now routinely being employed by academics, governmental agencies and private industry (Goodchild et al., 1993; Kovar and Nachtnebel, 1993; Longley et al., 1998; Burrough and McDonnell, 1998).
