I'm still waiting for a competition that syncs at least a bit with my free time. Mine starts in mid November
I like map from a base. Alternatively, I also like Skals's suggestion, although it has obvious limitations in terms of judging:
1. Map any location around the world. (rated on resemblance to the place and the difficulty of creating it)
I even know what I'd map, but how would the judges know it's accurate?
Ok, that's assuming they're not rich nor have plenty of time to travel around the world.