When you press "E", the editor command window pops up, but I definitely know that is not new. But, what is new is that you can flatten your map in two easy steps, by using a command available in that window.
From the editor command menu, select "Modify terrain". Then, drag from the northern point to the southern point or vice versa (or from the eastern to the western point or vice versa).
It would look as if you're selecting nothing, but in actuality, you are selecting the entire map by dragging from one corner to an opposite corner. Then, after you've dragged from one point to the other, press CTRL+SPACEBAR to flatten the selection, et voilą!
[EDIT] You could just use SPACEBAR, instead of CTRL+SPACEBAR to smoothen the surface, but if you want to start with a flat map, that is not recommended.
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[This message has been edited by Darkmaster (edited 02-28-2003 @ 07:13 PM).]