just because the area is square on your pip boy map, that doesn't mean its area that was suppose to be part of the playing area, the map area is more oval type shape not square, thats only how it looks on the pip boy, the area is still huge, easily as much area as FO3 even though it used a square playing area the overall playing area is about the same, the "square" map in the pip boy is larger than the fallout 3 area, its just they made the playing area oval so not sure why you can't figure that out, if they wanted the playing area square they would of made it square, the playing area is not the same geographical shape as FO3, so don't try to compare and say oh boy they're both square but in new vegas you can't go in the area.
The play area seems smaller. There is a hilltop near Primm Pass, and from it, you can see all of the southern half of the map, and you can see how close the towns really are to each other. They seem further away because we always have to walk around hills, etc. There is nothing West of the ridge line at Goodsprings. You can get through there and although the ground is rendered, there is nothing...no mobs, no structures, etc. That is, an awful lot of the pipboy map is unplayable.