revealing a Mini map, how to??

Hi there, I dont know if there is an easy way to do it but what I want is a game map that reveals itself as the character explores the scenario and that the revealing map information are stored, so if I return to a pre-visited map the exploration data will be there just like toe jam & earl (sega genesis), is there a way?

Thanks a lot in advance!

http://answers.unity3d.com/questions/7409/how-would-i-do-fog-of-war