If you find that you have saved over a wrong map, or you've made an error editing the map and have already saved, you may want to return to a previous version of the map. Each time you save a map, Driftmoon moves the previous map to the map backup folder, located at: Documents\Driftmoon\map_backup
That folder hosts each of your previous map saves, and it can get quite large, so you might want to empty it from time to time. The maps are named like this: "test.map_08.09.11_08.55.02.backup". When restoring the map, all you need to do is to rename it like this: "test.map", and copy it to your Driftmoon mod/maps folder.