For quite a long time now I've had a campaign world thought up in my head, and even had a go at mapping something out a few years back. The basic concept is that after a cataclysm, the game world is something of a waterworld; giant helical seatrees, tall coral pillars, sprawling seaswamps, the occasional giant mangrove tree, rare volcanoes (the last testament to a foundation beneath the water), and the gravity defying floatstone islands. Everywhere else is the sea, having long since flooded over the landmasses of the world. If the peoples of this world regained civilization (as they do in the campaign), and gained a way to travel beyond the scrap of land, coral, or wood they cling to (which they do), they would eventually need maps.

Here is the beginning of my map, a small archipelago of some of the features I listed earlier. This is just a small section of a much larger sized map, but presented at 1:1 pixel ratio.
Click image for larger version. 

Name:	ArchipelagoWIP1.jpg 
Views:	105 
Size:	112.5 KB 
ID:	25715