From Bulbapedia, the community-driven Pokémon encyclopedia.
Each location in the Generation II games has its own ID used internally by the game.
These IDs and names are used by Pokémon Crystal's Poké Seer in Cianwood City. She recognizes IDs 0x81-0xDF and 0xFE-0xFF as being the same locations as IDs 0x01-0x5F and 0x7E-0x7F.
- For all IDs not marked (unlabeled) in the table below, she simply says, "Hm… I see you met <Pokémon> here: <location>!"
- Any IDs not included in the table below use the same response, but since they do not have valid strings associated with them, the location name will be gibberish.
- ID 0x80 is recognized by the Seer as Unknown.
- IDs 0x00, 0x7E, and 0xFE cause the seer to say, "Whaaaat? I can't tell a thing! How could I not know of this?".
- IDs 0x7F and 0xFF cause the seer to say, "What!? Incredible! I don't how understand how, but it is incredible! You are special. I can't tell where you met it, but it was at level <level>. Am I good or what?"
IDs 0x60-0x7D and 0xE0-0xFD are completely invalid.
In Pokémon Crystal, the location header pop-up at the bottom only recognizes IDs 0x00-0x5F; all other values return gibberish.