From the point of a 3D engine programmer:
It is not wise to create a very detailed and ridged surface, because in the far distance, the details get reduced (to save calculation powers), and the \"Level of Detail\" changes would pop around remarkably with too many details.
Also, it is wise to reduce the lines of sight - the less one can see, the less it must be calculated, the faster it renders.
Furthermore, from the point of a game developer:
A player should not see the whole place at once. He needs time to learn the topology. He shall be afraid to get lost, until he can afford to explore. Therefore, it was a good idea to make the road like a deep valey, hard to climb except for a few places.
Finally, from the point of a citizen:
At some places, dirt rinsed from the ceiling of the hollow stalag, being dragged around by some wind inside, probably. This way, hills formed over thousands of years - steeper here, flatter there. Maybe even a river streamed through the hills once (and probably created the first hole in the Jade Gate of Korogan - the hollow stalag portal), but now everything is dry there.
I hope that this is a good explanation for everyone who would like to accept it, at least partially. I don\'t like to make such efforts for people who love to query and deny everything...
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A word to the developers:
There must be different heightfield maps to a) display the hills, b) calculate the walking height. Sometimes I walk up into thin air, sometimes I walk down through the ground. I investigated the zip file and found 4 distinct heightmap images, and they differed slightly.