Terrain MaskBasic Shader
The Terrain Mask can almost be compared to the Falloff shader, only that the Terrain Mask offers a great deal more settings that are especially designed for rendering landscapes and terrain. What this shader primarily does (e.g., in conjunction with the Layer or Fusion shader) is mask out regions that exceed or fall short of specific height or angle values. In the image above a snow texture is masked out on steep terrain as well as at lower altitudes.
Grass can also be included on flat terrain, which mostly lies in lower regions.
You can also use the Terrain Mask in conjunction with a Clone object and a Shader Effector, for example to let trees grow only at specific altitudes: