Three pieces make the map. There is a Central Slab in the middle and an End Slab on either side. Change those pieces and the same training facility becomes a different battlefield. Activision puts the number of possible launch configurations at more than 500.
That doesn't mean learning a section is pointless. Some borrow from Crash, Storage Town and Shoot House. You may know the cover in front of you. The catch is what it connects to. Knowing where an enemy could come from last round won't necessarily tell you where to watch now.
How the rounds work
The launch offering includes 3v3 and 10v10 Gunfight. Both teams receive the assigned weapons and equipment, with no custom loadouts. They swap sides after the first round. After the second, a new arrangement arrives, along with another loadout. The reshuffle repeats every two rounds until a team gets six wins. An overtime flag breaks the deadlock if neither side has been eliminated in time.
Xbox Wire's launch report suggests learning the centre first. It connects to the other sections, so it is a useful place to begin making sense of an unfamiliar arrangement. The official Call of Duty overview also describes weather simulation and routes over containers, roofs and balconies.
What we'd watch for
The difficult part is keeping all that variety understandable. A new angle can create a good surprise. A death from a doorway nobody could reasonably spot is a different sort of surprise. How well players can read a fresh layout matters more than how many layouts fit on the list.
There is an interesting little rivalry built into the side swap, too. Get caught by a position in round one and you can approach it from the other direction in round two. Then the sections change. There isn't much time to get comfortable.
Kill Block's Gunfight matches are available now in Modern Warfare 4 on PC and consoles. More core multiplayer modes are planned for the arena after launch; they aren't part of the confirmed starting lineup described here.