Well they could never represent a city correctly, because the map would be huge, the citadel or pentagon is surrounded by a huge carpark in reality, plus the riverside frontage is incorrect, plus from the capital building to the lincolns memorial goes up to the edge of the potomac and buildings dont block the way to the whitehouse, theres a lawn which leads from the washington monument, plus the rear of the capitol building theres some major buildings missing. Arlington national cemetary is right next to the pentagon as well, and arlington house isnt a wooden residential building. Im from Australia but was going to run pen and paper rpg fallout 3, so i did alot of study of the maps of the area to get locations correct.
But no basically its their representation of dc for the purposes of the game, same as new vegas, the vegas strip is completely different, the place names are pretty well correct though, just not exactely in the correct positions due to game limitations.