From Bulbapedia, the community-driven Pokémon encyclopedia.
Each location in the Generation IV games has its own identification number used internally by the game. They are enumerated here, in order.
These identification numbers are only used in Generation IV, and are not used to determine the location on the status screen of a Pokémon that is transferred to Generation V - this is instead generated based on the game in which the Pokémon was created, being "Sinnoh" for Diamond, Pearl, and Platinum and "Johto" for HeartGold and SoulSilver.
Locations with index numbers up to 0111 appeared in Pokémon Diamond and Pearl, those with index numbers between 0112 and 0125 appeared only in Pokémon Platinum, and those with index numbers between 0126 and 0234 are exclusive to Pokémon HeartGold and SoulSilver. Index numbers between 0235 and 1999, 2015 and 2999, and above 3076 are filled with null data, while others are "special" locations for Pokémon exclusive to events and the like. If a Pokémon references an index number for met location that the game it is in cannot understand (due to the location data not being programmed in), it will be displayed in that game as "Faraway place". Later-released games of Generation IV have all location headers programmed in that their predecessors do, meaning that HeartGold and SoulSilver will display the met location for all Sinnoh-native Pokémon, but Diamond and Pearl will display "Faraway place" for any Platinum and HeartGold and SoulSilver-exclusive locations. Though there are pointers for "Johto" and "Sinnoh", these are not used for Pokémon caught in these respective regions.
- Programmed into the games are locations for potential future event Pokémon given away all the way up until 2016, including one for the 20th movie. As events for the 14th movie and onward have been exclusive to Generation V, it is unlikely these will be used.