I am posting a guide for this because if it is too deep, the game lags up! I have seen some very good maps which have been ruined because of it!
This is quite a complex guide but it works and it is the only way I have found so far! Some of the steps may sound a bit strange but don't worry! Save it before you do this trick incase you mess up!
(1)Flatten the entire map to highest you can! (try to flatten it all without letting go of the mouse button because you will see why later)
(2)Go to world/map elevation:
If you have the new editor:
press the MAX button loads and loads of times.
Old editor:
press the move map up button tons of times and press apply
You need to do this loads of time if your on old editor because map dosn't move as much when you use that function.
(3)playtest the scenario - no need to save it.
(4)go back to editor and you will see the cliff stuff has disappeared!
(5)press the UNDO button and all your elevation will return to normal!
Press it more than once if you didn't manage to flattern the elevation in 1 go.
Thats it!
You can also do the opposite and get really high cliff on side of map too but only do this on SMALL maps or it will lag!
Very useful guide and I have fixed several peoples maps by doing so.
Please comment on this guide.
This is partly from an old guide I made but it was way too confusing so I changed bits and added the screenshot.