Minecraft wiki entry for Development_versions, associated text: Maps now align to a grid, making it easier to create adjacent maps.
A compass and paper do now create an empty map.
An empty map has no data on it until the player right click with it.
The point on the player's world where the player right clicked it is the map's center.
A map (with data) can be cloned. Cloned maps are stackable.
Maps can be zoomed out (but not zoomed in).