Hmmm, there's one more idea: basic, player's initial map (with "i'm here") can be upgraded through advanced maps, you've mentoined up there So, player will have two ways of opening uncharted areas or unknown details - firstly, go there and find out everything himself (long way), secondary - buying expanded or detailed maps from other players/NPC (expensive way). Amount of efforts should be about the same.

P.S.: There's a good idiom in Russian, that can be translated like "Rabbit cultivation manual". So ..