The Pokémon Diamond and Pearl region of Sinnoh was inspired by the Japanese island of Hokkaido.
Diamond and Pearl are set in Sinnoh, a fictional region characterized by snowy routes, mountains, lakes, and a large underground area. Its geography reflects Hokkaido's northern setting and gives Sinnoh a colder visual identity than many earlier Pokémon regions.
Mount Coronet divides Sinnoh into eastern and western sections, while three major lakes—Verity, Acuity, and Valor—form an important triangular arrangement in the region's mythology and geography. The Sinnoh Underground adds a network of caves and tunnels beneath the overworld.
Sinnoh is not a direct copy of Hokkaido. It adapts real geography into a fantasy setting, as other Pokémon regions also draw on real places. Diamond and Pearl were released for the Nintendo DS in Japan in 2006 and introduced the franchise's fourth generation.