Problem with a map.

[Perturabo]

I'm trying to create a fort with a dry moat with two small forts inside the moat that would be able to fire only inside it.
The moat is supposed to be on height of 370m, the surrounding terrain on height of 400m, and the firing part of the fort on 430m.
The problem is that the moat ends up on the level of of surrounding terrain - 400m or even higher.

http://i.imgur.com/QJPjqyr.png

[RockinHarry]

There´s terrain/height smoothing coming into effect and terrain feature accuracy depends how much of any the layers outlines touch or intersect with the invisible 100m grid below. Thus you can´t have totally accurate map terrain/heights at this scale and it´s better to sacrifice some accuracy and adapt map features to the mentioned 100m grid, if necessary.