Rocksteady games head Sefton Hill has stated that Arkham City will be “five times bigger” than the Arkham Island seen in the first game. In an interview with Gamespot Hill went on record saying “The footprint of Arkham City is about five times bigger than Arkham Island, but our primary intention was never to create a bigger gameworld just for the sake of it. In Batman: Arkham Asylum, we really focused our effort on creating an intense, pressure-cooker atmosphere by locking Batman in the madhouse and allowing The Joker to turn up the heat.”
He also added that “in Arkham City, we want to take that attitude to the next level, so we created an experience in which gamers will have a huge amount of navigational freedom, but they will also feel the extreme pressure of the challenges that they face. Players will be able to go anywhere at any time, but we have made sure that players will always have a very clear idea of where they are needed most if they want to just stick to the core narrative path of the game. Explore the streets of Arkham City, and you will find many side missions, secrets, and street brawls, so players won’t find it difficult to get into some trouble if that’s what they are looking for.”
Thanks to VG247 for the info.