Yes, exactly.
Simple. I've pretty much mastered the map editor so if anyone wants help, just ask.
Create your land area, now create a second land area within that land area. Now copy the entire area, paste it and the pasted area will have a hole where you create the second land area within the first. Copying and pasting has alot of neat tricks.
The Uk for instance is one land mass despite separate land areas. By copying and pasting, you unify the land masses as one.