Slagtown is the slum area which is directly south of (and connected to) Freedom City. Slagtown is a little seedier and more dangerous than Freedom City, and is, for that reason, not protected by the Freedom City Police Department. Once you venture outside of Freedom City, you'll be responsible for your own defense.
Notable landmarks include:
Rolf's Gym: Designated RG. Contains Speed Bag, Weight Set, Rowing Machine, and a Hot Tub in the front, a Cardiogram and a Climbing Wall in the back.
Sargo's Discount Warehouse: Designated DW. Sells random recycled items from evicted apartments at very low prices. Usually filled with junk, but occasionally great items can be found. Stock refreshes every 10 minutes.
Bradbury: Designated Br. A budget apartment complex right on the doorstep of Freedom City. There is a trapdoor to the cellar where zombies can be found.
Princeton General Hospital: Designated by a red + on a white background. Generally used to train medic by healing the various patients wandering within. An operating table and an implant extractor can be found on the third floor. A trapdoor leading down can be found through search in one of the rooms of the first floor, a light is needed to navigate below.
A detailed map with descriptions can be found here.