The editor has the ability to store a 'pad image'
You can use any picture you want, and place it as the bottom layer of your map.
Here's a google earth map of US Western seaboard I choose to use as my 'pad image':
Drawing some roads, railroads, and rivers with the editor:
Drawing significant terrain features, such as forests, country-sides, the Rocky Mountains and Sierra Nevada:
How the map will now appear in game, a near perfect likeness to the real world geographical layout.
