Invisible Barriers, also known as Invisible Walls, are preventative measures integrated into the game to prevent the player from leaving the game world. This feature can be found in 3D Universe games and above. They can kill the player in a variety of ways, from just blowing up the player in a boat to taking a wing off a player's jet. There are three types of ways the player can be killed by the barriers.
All GTA games in the 3D Universe have similar mechanics for keeping the player confined to their game world.
In GTA III and GTA Vice City, if the player flies far enough outwards towards the ocean, after reaching a certain point, the game will immediately turn the player's vehicle around. For example, if the player flew a Skimmer straight north in GTA Vice City, after a few minutes, the Skimmer will suddenly be turned around, so it is pointing the opposite direction, but it will still be going the same speed as it was before. GTA Liberty City Stories and GTA Vice City Stories retain this feature. However, in GTA San Andreas, the world technically lasts forever, as oceans generate as the player flies far enough from the game world. This was done because the player has to go to Liberty City in the mission Saint Mark's Bistro.