What do you call the lines on a topographic map that indicate the elevation of the land forms?
They are called "contour lines".
The contour lines are used to indicate the elevation on topografic maps. Usually, we use two types of lines to represent the landforms in a map. The regular line and the master line. The master lines, or master contours, are used to indicate, graphically, the elevation of the seccion of the relief, and they are represented in a different color on the map.
For example, in the map, below the contour lines are represented in red, and the master contours are represented in green.