Anacostia Crossing

 and nearby Rivet City is the most southeastern area of the reachable map.

This is the area where Rivet City can be found at; the southernmost tip resting against the banks of the river. Also, the Anacostia Crossing Metro Station is located near the tower linked to Rivet City. The station and tunnels are inhabited by several lightly armed Raiders. The northbound line terminates at the Museums.

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.