It is, in fact, a mini map, but you don't have a whole lot of control over your movement. Each square on the minimap is at least 2 maps of space, and you can't ever backtrack without finding a loop or casting return. Your only overworld movement decision is whether to take the grey or white door when both are present-- they will generally lead in the direction that would make sense, but you can check the minimap for that as well-- there's no marker for where you are, only where you can move next.