That's cool looking. How did you sculpt that? In AC3D or Blender or L3DT?

1. Made a 2048x2048 bitmap with a rough plan of the hills, using Paint.net. Could also use MS Paint, but Paint.net has layers, which was useful in laying out a grid and main gun range radii.
2. Import that into L3DT, set to 2048x2048 and a scale of 660 meters.
3. Use L3DT to add detail to only the right half of the object. Left the other half alone.
4. Export Active Map Layer to OBJ format.
5. Import OBJ file to AC3D.
6. Scale it down by 1.5625%, then snap the whole thing to grid.
7. Delete the left half of the object polys. Change color of the upper half of the right side to red, just for ease of moving it around.
8. Replicate the right half, so you have a balanced mirror image, then connect the two.
9. Center it on the origin.
10. Clean up any gaps or whacky polys.
What you end up with is a 4 mile by 4 mile object, with vertices spaced at 660 feet. The whole process takes about 45 minutes.