"Visit the Alola Region! Your new adventures in Pokémon Sun and Pokémon Moon will take place on the tropical islands of the Alola region! The Alola region centers around four islands rich in natural beauty and an artificial island. Many Pokémon that have never been seen before occupy these islands."
(pokemon-sunmoon.com)
The Alola Region consists of four main islands. The clouds shown in the map may hint at previous Legendary Pokémon, those being Ho-Oh and Lugia.