How can I make a minimap?

I'm working on a game that will need a minimap and will make heavy use of it. So far I am clueless as where to start. So far I was thinking it would be on the touch screen or on the same screen and I can open it up. My question is, where do I start when making a minimap and what's a good method for creating a minimap?

Take your in-game image data (Sprite x,y positions, etc.) And re-represent it in a simpler form, like on the graphics screen.