Kanto Region

"The Kanto region is a region of the Pokémon world. It is located east of Johto, and as revealed by the radio show Sinnoh Sound, is located south of Sinnoh. It was the first region to be introduced. It is the setting of the Generation I games and FireRed and LeafGreen; it is also accessible in Pokémon Gold, Silver, Crystal, HeartGold, and SoulSilver after the quest in Johto is completed.

All cities in Kanto are named after colors (Viridian City, Lavender Town, Indigo Plateau, etc.), with the exception of Pallet Town, which is also a reference to color. Professor Oak is the resident Pokémon Professor and gives Pokémon Trainers a choice between Bulbasaur, Charmander, or Squirtle as their starter Pokémon. In Yellow, the only choice is a Pikachu that he recently caught, although he did have an Eevee. In the games, the player begins his or her journey in Pallet Town and ends it at Indigo Plateau."

This excerpt is directly from the "Kanto" Bulbepedia article and was written by members of the Bulbepedia community. The full "Kanto" article is available at Bulbepedia.net.

Johto Region

"The Johto region is a region of the Pokémon world. It is located west of Kanto, and as revealed by the radio show Sinnoh Sound, is located south of Sinnoh. It is the setting of Pokémon Gold, Silver, Crystal, HeartGold, and SoulSilver. Johto and Kanto are part of a large landmass, with everything west of Indigo Plateau falling in the Johto region. Though it is unlike Kanto in that its name is not directly based on that of a region of Japan; Junichi Masuda has stated in his director's column that the kanji that inspired the name mean "castle palace" or "lattice-shaped palace"; this meaning is connected to the city of Nara, which was the basis for Violet City.

First explored in Pokémon Gold and Silver, it is home to an additional 100 Pokémon that were not present in the previous games. Players begin their journey in New Bark Town, where Professor Elm offers either Chikorita, Cyndaquil or Totodile to beginning Pokémon Trainers. The English-version names of most of the cities in Johto are also the names of plants or things related to plants."

This excerpt is directly from the "Johto" Bulbepedia article and was written by members of the Bulbepedia community. The full "Johto" article is available at Bulbepedia.net.

Hoenn Region

"The Hoenn region is a region of the Pokémon world. It is located south of Sinnoh. It is the setting of Pokémon Ruby, Sapphire, Emerald, Omega Ruby, and Alpha Sapphire. It is inspired by the real-world Japanese main island of Kyushu. The names of most of the cities in Hoenn are made of two words put together (Little Root, Fort Tree, Slate Port, Ever Grande, etc.) rather than colors or plants as Kanto and Johto had done. Professor Birch of Littleroot Town offers the starter Pokémon known as Treecko, Torchic, or Mudkip to Trainers beginning their journey of this vast land."

This excerpt is directly from the "Hoenn" Bulbepedia article and was written by members of the Bulbepedia community. The full
"Hoenn" article is available at Bulbepedia.net.

Sinnoh Region

"The Sinnoh region is a region of the Pokémon world. It is located north of Kanto, Johto, and Hoenn. It is the setting of Pokémon Diamond, Pearl, and Platinum. It is comprised of the large mainland, the north-eastern island of the Battle Zone, and several smaller islands on both sides of the region. Most of Sinnoh's routes are on land, having very few water routes, in vast contrast to Hoenn. The region is divided by Mt. Coronet, roughly comparable to how the continent that Kanto and Johto make up is essentially a contiguous region."

This excerpt is directly from the "Sinnoh" Bulbepedia article and was written by members of the Bulbepedia community. The full "Sinnoh" article is available at Bulbepedia.net.