The geographical data subsystem consists of two parts:

• a maps base which contains maps with two possible structures :
• a Raster structure represented by an array of pixels and
• a Vector structure represented by a collection of vectors,
  
  
• a maps module to manage maps:
• vector-to-raster and raster-to-vector transformations,
• files transfer,
• maps display images processing...
  
  
  

 Maps can represent two kinds of data:

• qualitative data where each spatial unit is characterized by a nominal or an ordinal characteristic. For example, a soil occupation map can be classed in four classes such as
• 1: forest,
• 2: culture,
• 3: wetland,
• 4: urban area;
  
  
• quantitative data where each spatial unit is characterized by a cardinal characteristics. For example, a rainfall map contains data from 0 to 1000mm.