The DTM is a homogeneous and regular point grid indicating the elevation of the ground level in order to make a model of its surface. The DTM is drawn up by interpolation (adaptable prediction) of raw altimetric data (contour lines, structure lines and spot heights).

The contour lines contain all lines which connect points which are situated on the same altitude, in a model which is used to represent the relief on a large scale.

The contour lines contain all the lines connecting points with the same elevation, in a model which is used for a cartographic representation of the relief.