Slag Pits is a 4 player map.
Metalopolis was one of two favorite maps across the different skill levels of players. Blizzard decided to introduce a very similar map, but slightly more macro heavy. Blizzard took out Shakuras Plateau, which was a very plain macro map, and added this map instead. Some of the key features of this map are the low-ground high-yield expansions, the two lines of shrub area that can be used to position units, as well as the low-ground watch tower that watches over all of the low-ground center.
Blizzard Entertainment. StarCraft II. (Activision Blizzard) Map: Slag Pits (in English). 2011.