Altitude range (DM parameter)

The 'altitude range' slider in the design map parameters wizard determines the steepness of your map.

This is demonstrated below, where where I've made terrain with altitude range settings from 0% up to 100%:

Altitude range	Design map	Heightfield	3D render
0% (left, flat)
25%
50% (centre, default)
75%
100% (right, steep)

The height range of the terrain is also affected by the feature scale setting.