General
The Triangle: Kanto, Johto, and Sinnoh are the three main countries making up the massive Triangle island. There is at least one other country in the mix, too. A small country called Rota.
Sterling: A massive mountain range separating the countries of the Triangle, causing it to be shaped like a cross. It gets its name from the tallest mountain in the range being Mt. Silver, named after a tradeable currency.
Kanto
Venture Forest: The forest surrounding Pallet.
Old Pallet: In the North-West of Venture Forest is a destroyed town. The inhabitants moved South to the coast and made a new town with the same name, Pallet.
Amethyst: A town on the coast North-East of Pallet. Someone from Old Pallet found a cave near a beach. The cave was rich in gemstones and, with his favourite being purple, he founded a beach town.
Johto
Gloriosa: A city at the Western most point of the country. It was founded a couple of centuries ago by Galarians who sailed East and reached Johto.