Thematic cartography today: recalls and perspectives

The starting point for this article is the fact that each spatial object i is characterized by three coordinates: x (latitude), y (longitude) and zi(by tradition elevation). The discussion is organized around three axes. First, the author reviews some of main problems encountered when representing a volume (ellipsoid) on a plane (map). Second, some elementary principles of cartography are discussed in order to demonstrate the importance of the nature of z in thematic mapping. Third and last, the author shows how the realistic representation of the third dimension can be improved by use of visualization techniques, a modern discipline that is close to but different from cartography.