A universe can be considered a completely separate 'canon' of places, people and events that do not exist in the other universe. Locations that appear in multiple universes are completely rebuilt, rather than just updated. A previous universe would be like a mythical universe that never really existed.
However, some things do exist appear in multiple universes, including company brands, vehicles and weapons.
Universes are closely linked to Eras, which are logical groupings of the games based entirely on their number (i.e. GTA III starting the GTA III Era). Within a single era, many things are shared, including visual styles, game engines and most features. Between different eras in the same universe, fewer things may be shared, such as just the visual style and some minor characters..
|2D Universe||3D Universe||HD Universe|
|GTA 1 Era||GTA 2 Era||GTA III Era||GTA IV Era||GTA V Era|