File \ New Map
Once you have setup a "Clean Maps Directory" (see Tools \ Settings), this will allow you to copy a clean map to a new file name in the "Maps" and will also give you the opportunity to internally rename the map.
Select a base map, then enter in the new filename. If you wish, you can change the New Map Name (Internal Name) at this point. By default it will name it internally to the new filename.
After pressing "Create Map" a copying dialog will show briefly, then the preceding information box will tell you the new name and the new map will be opened for editing.