The first map is called Standoff. It is described as a two base map with some vehicles and turrets.
The second map is named Rat's Nest. It was inspired by the campaign level Crow's Nest and is a primarily indoor map. There are vehicles on the map but expect some tight spaces as well. Ideal for 6-16 players and should be added into the Big Team Battle games.
And the last map is Foundry. Developers expect gamers to have a lot of fun with how much you can change this map in Forge. This level was inspired by the campaign level where you fight the Flood in the warehouse(the level where you should definitely NOT kill the wounded Marines, Josh). Developers say this is a good map for 4-12 players.