With the Generation II location digits covering 65536 maps (two bytes), could it possible that at least one of these maps take their data from RAM?
Also the first digit for the map as well is apparently the bank. I don't know the Game Boy well enough or have tested anything to assert this, but could out of bounds banks represent RAM?
You can access glitch maps with 01xx00DA, 01xx01DA (requires being in a Pokémon Center going up the floor and back down) or 01xx44D0, 01xx45D0 (walk through a door) (Gold/Silver) or 01xxB5DC 01xxB6DC (Pokémon Center floor requirement) (Crystal).
Would be cool if we could have our own town to go to without having to modify an existing one. :)