3.3.4 The geometry

In a GIS, data appear as geometries and tables and are represented in different ways depending on the data type. Three types of geometries exist to represent geographic objects:

• Points to represent point features (cities, projects, water points, etc.)
• Lines to represent linear objects (rivers, roads, etc.)
• Polygons to represent area elements (municipalities, zoning, land use, etc.)

Geometries in a GIS

The choice of geometry to represent data can vary depending on the scale of visualization.

For example, it is preferable to represent hospitals on a map of France by points. On the other hand, at the scale of a district, one can use polygons to represent the ground area of the hospital buildings.

Varied use of geometries for the same data