Rocksteady say that 80% of Arkham City will be set in the streets of Gotham. The other 20% will take place in interiors tied to certain missions, but for the most part, players will have a large amount of freedom to explore from the very start of the game.
Rocksteady told PSM3 that creating Gotham has been a "huge technical challenge," but the increased team size has helped them to pull it off. There are 97 people working on Arkham City, compared to 65 on the first game.
Rocksteady have previously said that Arkham City will be five times larger than Arkham Asylum, but the team say that doesn't mean the game will feel more empty.
"Our objective was not to make a bigger game world just for the sake of it. We want to fill it with content, and there's no better world than Batman's universe to take inspiration from.
"Because we've decided to make such a large world we had to bring in more artists, animators and so on. It's been a pretty huge technical and creative undertaking for the team."