From Bulbapedia, the community-driven Pokémon encyclopedia.
Each location Pokémon Colosseum and Pokémon XD: Gale of Darkness has its own identification number used internally by the game, mostly to display where a Pokémon was caught. They are enumerated here, in order.
As none of the locations in Orre correspond to locations in Kanto or Hoenn, Pokémon traded to any of the Generation III handheld games will display "met in a trade" as their captured location. When transferred to Generation IV, Pokémon will, like with Pokémon caught in the handheld games, use the game identifier to mark the Pokémon as being from a "Distant land", rather than "Orre".
Pokémon Colosseum and Pokémon XD both have locations for the same index number in multiple instances; this means that if a Pokémon is traded to a Game Boy Advance game then to the other Orre game, met locations for Pokémon met in the other game may be incorrect even if the location exists in both games. In the following table, indices not listed will display "met in a distant land" or "met at a distant land" in both games.