Regions

Pokémon regions areas in the fictitious Pokémon universe where everything Pokémon takes place. There are several Pokémon regions throughout the anime, games, and manga.

Pokémon regions and the Video Games
In the Pokémon games each generation generally takes place in the same region, with the exception of the second generation Pokémon Gold and Silver where the Kanto region (three years in the future from Pokémon Red and Blue) is available after defeating the Johto story-line. Besides this the closest to inter-region gaming that has been implemented is through trading, battling, and migration/importaton.

Kanto
The main Pokemon regions in the games are Kanto, Johto, Hoenn, the Sevii Islands, and Sinnoh. Kanto is the central story-line location in Pokémon Red and Blue and Pokémon FireRed and LeafGreen and is also accessible in the later portion of Pokémon Gold and Silver after completing the greater majority of the Johto story line. In Pokémon Ruby and Sapphire.

Johto
Johto is connected to the West of Kanto and is the central location of the Pokémon Gold and Silver story-line. The only interactivity Pokémon Red and Blue had with Johto was by trading through a "time machine" in GSC as long as there were no Party Pokémon in the GSC game with a PokéDex number higher than 151 (Mew) or moves not in Red and Blue. Gold and Silver were never remade on the for the GameBoy Advance so Pokémon Ruby and Sapphire, Pokémon FireRed and LeafGreen, or Pokémon Emerald could not even trade with the Johto region. Pokémon could only arrive from the Johto region in the GBA games through cheating. The GameCube games are the same as GBA games when it comes to Johto.

Hoenn
Hoenn, to the Southwest of Kanto is the central location Pokémon Ruby and Sapphire and Pokémon Emerald. Pokémon from Hoenn could be moved to the GameCube's Pokémon Box: Ruby and Sapphire, traded to/from Orre (in Pokémon Colosseum and Pokémon XD) or the Kanto region in Pokémon FireRed and LeafGreen, but no other region (besides the Battle Frontier, the Event location Southern Island (in Ruby, Sapphire, Emerald, FireRed, and LeafGreen), the Event location Southern Island (only in Ruby, Sapphire, and Emerald), and the Event locations Faraway Island, Birth Island, and Naval Rock (available only in Emerald, FireRed, and LeafGreen).

Pokémon caught in Hoenn can be migrated to Sinnoh in Pokémon Diamond and Pearl and Pokémon Platinum. The process of migrating moves the whole Pokémon to Pokémon Diamond and Pearl and Pokémon Platinum and cannot be later accessed.

The Sevii Islands
The Sevii Islands are 7 Islands accessible only in Pokémon FireRed and LeafGreen (9 including the exception islands accessible in Pokémon Emerald: Birth Island and Naval Rock). They were not introduced until after Pokémon Ruby and Sapphire, therefore Pokémon FireRed and LeafGreen and Pokémon Emerald are the only two games that can directly access any/all of the Islands. Pokémon captured here can still be moved/traded to Pokémon Ruby and Sapphire, Pokémon Box: Ruby and Sapphire, [Pokémon Colosseum]], Pokémon XD and migrated to DPP.

The Sevii Islands
Sinnoh, based of Hokkaido, was introduced in Pokémon Diamond and Pearl and is the central location of Pokémon Diamond and Pearl and Pokémon Platinum. Pokémon can not be traded from Sinnoh to Kanto, Johto, Hoenn, or Orre. Pokémon in Pokémon Ruby and Sapphire, Pokémon FireRed and LeafGreen, and Pokémon Emerald, however, can be migrated, or imported, to DPP after acquiring the National Dex. Migrated Pokémon cannot be sent back to the GBA games without cheating. All Pokémon Diamond and Pearl and Pokémon Platinum Pokémon can be transferred to/from Pokémon: Battle Revolution.

Other Regions
Orre, based off the Arizona desert, located on the NW porton of the Kanto-Johto landmass, is the generally Wild Pokémon free region in Pokémon Colosseum and Pokémon XD. Very few wild Pokémon can be captured in Pokémon XD, other wise Shadow Pokémon are "stolen" from the bad guys. This is the only Pokémon game where Pokémon can be stolen without cheating.

Fiore, located at the NE part of the Kanto-Johto landmass, is where Pokémon Ranger is set.

Almia, located East of Fiore, is where Pokémon Ranger: Shadows of Almia is set.

GB Island and GB Island 2 is where the Pokémon Trading Card Game and Pokémon Card GB2 video games are set, respectively.

Pokétopia is where Pokémon: Battle Revolution is set.

Stadium Island is where Pokémon Stadium is set and White City is where Pokémon Stadium 2 is set.

The Pokémon World is where humanless Pokémon Mystery Dungeon games take place.