I think the tmb is just map data, as in programing that is used to build the various locations in-game. They all have...
Code:
xsi scene root object
... in the coding and they have reference different pngs.
Doofenshmirtz: This is a little bit awkward but have you seen my escape jet keys? (Perry nods) What, you have? Well that's great! So where are they? (Perry looks away) You won't tell me? Is this because you don't speak or are you just being a jerk?
~Phineas and Ferb, "One Good Scare Ought to Do It!" (2008)
