There is an unused location that the game sets as a visited Fly location after it is visited. Its index number is 11, stored with towns and cities but before Route 1. This suggests it may have once been intended to be a main key area in the game. It doesn't have any Town Map data, and defaults to Pallet Town with coordinates of (0,0).
There are various maps with Town Map data which are otherwise completely blank. These locations may have been formatted maps.
Invalid maps 237-244 if forced to load in Pokémon Yellow load a glitch location (a 'cycling based glitch map') where the player character is forced to move across a white background with striped with blue bars. In other versions, these "maps" freeze the game.