Developer DICE has been babbling for awhile now about the Battlefield 3: Armored Kill map "Bandar Desert" being the biggest in Battlefield history. They said similar about the vanilla maps, though, so fans have been understandably skeptical. That's going to be difficult now, though, as DICE has pulled out the measuring tape and laid out exact figures for it.
In Conquest Large, if you count from your jet spawn zone to the enemy jet spawn zone, Bandar runs 2400 meters; if you count from your deployment to the enemy deployment, it's 1900 meters (even longer than Fushe Pass), and from the closest flag to the furthest flag, it's 1200 meters. By comparison, Caspian Border spans 1100 meters between deployments, and 400 meters between the furthest flags.
Console players won't be able to revel in quite the same scope as what will be seen on PC, but as ever, it's scalable.
Bad Company 2 lovers should be pleased to know Bandar is inspired by fan favourite Atacama Desert.
For an extensive read on the design and gameplay of Bandar, hit the source.