The sample project “The boy and his kite” contains auto-landscape material that is worth checking out. Also Brushify has a good one. You can find good tutorials showing the steps,which I can share it here if you need.
Typically you want these features:
- Tiling variation for macro and micro detail
- Foliage spawner with noise based variation
- Multiple landscape layers, inclusing an eraser layer for creating holes
- slope detection for blending snow with rocks or for limiting the areas covered with grass based on the maximum terrain slope angle, for instance.