Yo, how do I delete certain overlays or units or cities en masse without having to go through the tedious task of right click and deleting them one by one in Civ3QEdit?

Also note, I don't want to clear the whole map, I just want to remove certain overlays,units etc en masse without interfering with the rest of map.

You can right click on the group you wish to delete...
select the Delete option
select either Delete Unit or Delete Overlay (if Units or Overlays are available in that tile)
then it will show the units/overlays available to delete
and at the bottom it will have the option to: Delete All Units / Delete All Overlays

Tom

My editor includes such tools, to delete at once all pre placed units, cities, colonies, roads, etc.

http://stephane.f.david.free.fr/CivMod/Tools/ExpandedEditor/MapTools.jpg

My editor includes such tools, to delete at once all pre placed units, cities, colonies, roads, etc.

http://stephane.f.david.free.fr/CivMod/Tools/ExpandedEditor/MapTools.jpg

Thanks, saves a lot more time then deleting them individually.

Also, does it by chance do the same for city improvements?

Not yet...

If you want to remove ALL of a certain overlay, uncheck "Allow X" for all terrain types, close the rule editor, and go back and recheck them as necessary. When an overlay is disabled for a terrain it is automatically deleted from that terrain.