Anacostia Crossing

 is the most southeastern area of the reachable map.

This is the area where Rivet City is.

Inhabitants

 * Just west of here is a Super Mutant camp, but in general the area is empty - except for Carlos, asking for water near Rivet City.
 * For those interested in freeing all of the Captives, one of them is in the Super Mutant camp. The captive usually dies running along the scaffolding by Jefferson Memorial unless you've cleared it out, then again they all presumably die somewhere in the Wasteland after you free them