One of the reasons Rockstar went for an enormous world design in Grand Theft Auto 5 was so that they could accommodate flying in the game.
Dan Houser, co-founder of Rockstar and co-writer of Grand Theft Auto 5 spoke on the matter with The Guardian where he explained the necessity to have increased airspace.
We wanted to make a big place, as much as anything, to allow you to fly. A lot of the decisions, we’re talking about them here on a philosophical level, but they’re also practical decisions, too: we’re making a game. You have to understand the medium.
On an obvious level we wanted somewhere big so you can fly properly – we have a lot of missions that involve flying, in helicopters or whatever, it was logical. Also, Jet skis work better around LA than they would in New York.
We’re using the environment to let us have toys we couldn’t have had otherwise. And equally, we’re using the story and environment to introduce missions that can be more extreme. In some ways we wanted the game to have a larger-than-life Hollywood feel; the stories we heard in LA, we wanted to capture them in the game. If the place isn’t informing what we’re doing, we’re not using it correctly.