Geographical Information Systems are becoming increasingly important to geologists, geographers, and urban and environmental planners, amongst others. Although there is an increasing number of such systems available on the market, many questions of a theoretical nature need to be addressed, because of the inherently large amounts of data and the lack of appropriate models and languages. Also, there is a need for flexible and efficient usage of GIS, thus permitting their application in a broad range of new areas, such as navigation systems for transport and the automotive industry. ESPRIT...