Incredible concept. I love the fact that you can't perfectly draw the map. I also just love the idea of a cartography game.
I don't think the map should be toggled. It should just be on screen as once. And movement of the ship (I assume) doesn't feel great. And the final image should be your map compared with the real one.
The biggest difficulty of making this game is creating a good scoring algorithm because 1 to 1 real map vs. player's drawn map wouldn't work well with stuff like shorelines.
Great concept though, look forward to seeing a more developed game in the future.