terrain clipping style

[Duke]

I noticed there are two distinct behaviours when it comes down to display the levels of a map:
- slice horizontally through the terrain (eg. military_convoy)
- don't slice (eg. wilderness (actually, it slices 'a little'))

Of course, slicing is necessary whenever there is something inside the hill (tunnel, chamber, ...).
But is that the set rule or does it also depend on the mapper's mood ?

[Mattn]

wilderness would not be easy sliceable without increasing the brushcount a lot. that's why i didn't do it. in general it should be done like in military_convoy.