The parts of the function tree are as follows:

 

1- Fractal function which defines the overall shape of the terrain. Here I used just one node. Of course this could also be a more complex set up.

 

2- Projected Texture Node. This part generates the heightfield. The Contrast/Brightness node below lets you scale and offset (altitude) the heightfield

 

3- This segment defines the area which blends-in the heightfield.

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