PokéFiends

Gateway Island
Island One, or Gateway Island, is the first island in the Seafoam archipelago. Located at the southwest of the U-shaped island chain, Island One is the gateway to the Seafoam experience. Featuring sparse grasslands, a small village surrounded by forests, and the only civilian international airport in the archipelago, Island One mostly caters to the incoming traffic of Seafoam. The airport and main harbor both lead to Gateway City.

Payon Island
Most of Payon Island, also known as Island Two, has been left to wilderness, save the location on the eastern side of the island of the Gym for this island, and the small town that surrounds it. The rest of the island is covered by forests ranging from tropical jungles in the interior to deciduous pines along the rim.

Aitutaki Island
Largely undeveloped, Island Three serves as a resort location for the Archipelago, with carefully maintained beaches and numerous nature trails through the forests. Also called Aitutaki Island, deep in the woods in the center of the island, one can find the Gym on this island and the ice queen that inhabits it.

Sandestin Island
The main civilian population center of Seafoam, Sandestin Island is the most densely-populated and built-up island in the entire archipelago, featuring countless apartment buildings, shopping centers, hotels, high-rises, and businesses. Though largely many refer to it as its actual name, it is also called Island Four.

Giltella Island
The only island in the archipelago whose makeup continually changes, Island Five, or Giltella Island, is the second of the original two islands that the Seafoam Archipelago was created from (Island One is the other original island). At high tide, only a small sliver of the island lies above sea level, while the rest of the island is revealed at low tide.

Michtam Island
Also know as Island Six, this location contains Fort Michtam, the seat of the Seafoam Army's command and control, as well as another industrial zone dedicated solely to producing the war materiel cooked up by the R&D division of the military.

Commerce Island
The second population center of the Seafoam Archipelago, Island Seven, or Commerce Island, is much more of an industrial zone, containing most of the region's ports and military manufacturing plants. On the northwestern shore of the island, a small area has been set aside for the more affluent Seafoam citizens to set up their residences. This is where Island Seven's Gym, which doubles as a research and development center, is located.

Okaloosa Island
At the very end of the Seafoam journey and the Intercoastal Highway that connects the islands is Island Eight, known as Okaloosa Island, is a lonely little spit of land that contains nothing but the Island Eight Gym. One cannot even find a Pokémon Center on this island. It's recommended that you heal up at Island Seven's Pokémon Center and carry plenty of supplies before setting out for this island. Seafoam's military also conducts weapons test and evaluations on clearly-marked test ranges on this island.

Joint Base Oceanus
Arguably the most iconic aspect of the Republic of Seafoam is its massive floating military facility, which houses all of its armed forces and is the size of any major mainland city. Though it qualifies as a naval base, Seafoam's floating military base is cross-service, and includes all the facilities necessary for the complete support, upkeep, and housing of Seafoam's armed forces, which number close to around 750,000 including noncombat personnel.