Map edditor

well, i want to edit maps so that i know where mobs and bosses spawn, now i know someone ( thanks ) made a map of volcano and made purple circles to show boss/mob spawn. how would i go about doing this, does anyonw have a program designed to do this

Er, I think all they do is find the most "occurring" spawns in which that "boss" or specific item drops at then they make a unique picture maybe using paint or photoshop. So I guess you try finding multiple co-ordinates of the boss spawning at those coords then paint/photoshop it. If I'm wrong, someone other then the topic poster correct me.

ty