Location

Locations are areas that exist in the SS undefined.

Inkadia
Inkadia is the region in which Inkopolis, Octo Valley and Octo Canyon is located. It appears to be located in present-day Japan. Hammerhead Bridge connects Inkopolis to the Splatlands for residents to travel back and forth.

Inkopolis
Inkopolis is a city in and  inhabited by various species, most notably Inklings, Octolings and jellyfish. The city contains two areas that serve as hubs, Inkopolis Plaza and Inkopolis Square, as well as various stages where Inklings and Octolings battle for sport.

Octo Valley


Octo Valley is a hidden valley located near Inkopolis, which serves as the setting of the eponymous single-player mode of Splatoon. Octarians live in this valley within underground domes accessible through kettles.

Octo Canyon
Octo Canyon is a hidden canyon located near Inkopolis, which serves as the setting of the eponymous single-player mode of Splatoon 2. Octarians live in this canyon within underground domes accessible through kettles.

Deepsea Metro
The Deepsea Metro is a subway system running deep underground beneath Inkopolis that serves as the setting of the Octo Expansion in Splatoon 2. It is the home of the denizens of the deep, and is run by C.Q. Cumber. It is composed of various stations, most of which house test facilities.

Salmon Run


The modes Salmon Run in and Salmon Run Next Wave in  are set in stages located on islands far away from Inkopolis, on the other side of the ocean. Salmonids gather at these areas. These stages are:
 * Spawning Grounds
 * Marooner's Bay
 * Lost Outpost
 * Salmonid Smokeyard
 * Ruins of Ark Polaris
 * Sockeye Station
 * Gone Fission Hydroplant

Splatlands


The Splatlands is a location in Splatoon 3. It is a very hot desert located relatively far from Inkopolis. Splatsville is located within the Splatlands and is the main hub of the game. It is also the location of some stages and the Crater, a massive crater that has a structure similar to the Eiffel Tower.

Alterna


Alterna is a mysterious location under the Splatlands, which serves as the setting of Return of the Mammalians in Splatoon 3.

Inaccessible locations
There are also some locations that have only been mentioned, but aren't accessible by the player:
 * Calamari County - Mentioned as being Callie and Marie's hometown. It is very far away from Inkopolis.
 * Mount Nantai - Mentioned in Splatoon 2. It is a mountain near Octo Valley.
 * New Sardine - Mentioned in the twenty-first Sunken Scroll in Splatoon 2. It is stated that New Sardine is the location Callie's TV drama is filmed. It is also stated that Callie was spotted at the airport after wrapping up filming.
 * Arowana Castle - Mentioned in the fifth session of Marina's chat room.
 * Anarchy Avenue - Mentioned in the third Sunken Scroll in Splatoon 3. It is presumably located in the Splatlands.
 * Southgill Province and Tailfin City - Mentioned in the twenty-fourth Sunken Scroll in Splatoon 3. Tailfin City is a city of Southgill Province.
 * Chateaubateau - Mentioned in the twenty-fourth Sunken Scroll in Splatoon 3.
 * Anarchy District - Mentioned in the twenty-fourth Sunken Scroll in Splatoon 3.

Trivia

 * In HaikaraWalker, it is implied that there are at least 20 different countries in the Splatoon universe.

Etymology
The name "New Sardine" comes from New Orleans in Louisiana, USA, and sardine.