ABSTRACT
Geographical Information Systems (GIS) are computer systems for collecting, managing and analysing geographically referenced data, that is, data which are spatially referenced to the Earth. Data in a GIS are generally organized in maps and refer to different geographic features, such as hydrography, orography, and transportation network. Thematic maps concern one geographic feature while composite maps result from composing separate thematic maps, one for each layer. A topographic map is a largescale (i.e. 1:10,000 to 1:100,000) composite map showing relief, vegetation, hydrography and man-made features of a portion of a land surface (Kraak and Ormeling 1996). Managing topographic maps is a functionality available in many GIS applications.
