The Check Sheet is a map of sorts found only in Fortresses. It's useless by itself, but used in conjunction with a Torch and Pencil, it allows Pit to track his location. The Check Sheet is discarded when a Fortress is cleared. It can't be purchased in Stores; Pit must discover it as he's traveling through Fortresses, though it's possible to clear a Fortress without obtaining it.
In Kid Icarus, Pit must find one of these located in the Fortress. This, along with the Torch and Pencil, are one of the few items exclusive to Fortresses.
Here, it's referred to as the Map, and can often be found in Centurion statues. It functions in the same way as in the original game and can only be found in Fortresses.