Atlas is, at its core, a massively-multiplayer online (MMO) game. A large portion of the game mechanics revolves around sharing the world with other players. It is unknown at this point whether there will be a single-player option, though it seems likely given the existence of such in its older sister, Ark: Survival Evolved.
Grapeshot describes a 'proprietary server network technology' that is purported to allow players to sail between many servers as though they were one, creating a single, enormous world of roughly 45,000 square in-game kilometers.
The huge Atlas world is made up of grids (separate servers) that are part of a zone (biome). Each grid has multiple islands and when you leave the grid you change to a different grid within a few seconds. Each zone contains multiple grids.
Multiplayer and Online Information
Currently there are four Official servers: North American PvP Krakens Maw and North American PvE Hydra's Den, European worlds are also one PvP and one PvE.