From Bulbapedia, the community-driven Pokémon encyclopedia.
Each location in Pokémon: Let's Go, Pikachu! and Let's Go, Eevee! has its own identification number used internally by the game. They are enumerated here, in order.
Index numbers between 00054 and 30000, 30018 and 40000, 40078 and 60000, and above 60004 are filled with null data. If a Pokémon references an index number for met location that does not exist in that game, it will be displayed in that game as Faraway place.