This is a terrain shader node group which applies different materials based on the height and slope of the mesh which it is applied to. It also includes an ouput node which you can use to bake a texture that you can use as a density map for trees and grass.
The screenshots show some examples of what you can do with it. The textures I used are from poliigon.com and I used the PBR node setup from Andrew Price shown here (https://www.youtube.com/watch?v=V3wghbZ-Vh4).
The terrain mesh seen in the screenshots was created with World Machine (http://www.world-machine.com/).
The textures and PBR node setup are not included in the download. You can use the terrain mesh as you like.