The out of bounds in Fallout: New Vegas that is usable without glitches is HUGE, potentially about 5 times the regular map size.
Here is some images of the out of bounds.
http://i51.tinypic.com/2me1o8w.jpg
http://i56.tinypic.com/2zg8785.jpg

Them areas is huge, think of all the stuff that could be added with mods that use those areas, its quite fun to go around exploring too, despite it being completely bare.
I cannot get you a good screenshot of how big this is, because some of the heightmap data seems to be completely outside the heightmap that I seen in GECK, I counted going over 3 mountain ranges in the north before hitting the edge, but in the same route on the GECK heightmap, It only showed 1 mountain range.

Possibly space reserved for future DLC? If not, that's some good real-estate for modders to use.

I was going to make a thread kind of like this. If you look at your pip-boy and look at the world map, there are HUGE areas that you can't go to. It's kind of like lying to us :ph34r:

Oh look! I'm gonna go over there! Oh wait, some kind of force field is blocking my way!

THE ENCLAVES BACK. :ahhh:

The areas go even further than the Pip Boy map can even display. Your arrow leaves the map image and then leaves the blank area around the map and is no longer displayed.

its just there for ascetic, would you like to look at the border and see just the sky, it is not really decorated that well, also some room to mod

I think its more than there just for that. For example, with Oblivion, the border of the map was not very far from the edge, at that point you just fall through the ground (With the exception of Elsywer, which is a large area) With Fallout New Vegas the map goes out about five times further than is really needed for aesthetics. Aesthetics would be adding terrain up to the horizon, and I went much further than the horizon before reaching the map edge.
Even if you go very high up, from the edge of the map I could not see even half the way back to the playable areas.

It seems they have left a lot of space in the current game area and on the out of bounds map space for some DLC that is included in the game world, or for modder's use, also noticed a lot of buildings which have the potential for housing user made content , at least they understand that Bethesda has a terrific modding community and is willing to do the work to make the perfect game.

well from what I can tell NV is a very flat area ergo you can see more, well flat in some parts there are also some mountains, but still great place to mod, and I honestly doubt that it is going to be in a DLC, no DLC bethesda has ever released has actually expanded the map, it has created other, but not expanded, except for morrowind, but that might have been in the bounds, never played it without DLC

Judging from this map and the distances in the game, the map might actualy go out as far a Shady Sands or Vault 15
http://images1.wikia.nocookie.net/__cb20080606162927/fallout/images/2/29/Western_USA_v1.0.jpg

There are many flat places in between the mountains which are flat enough to use.

sooooo much free space! why didnt they use this. they coulda made New Vegas about 5x bigger n better and moved all the places back about 5 miles lol. and they coulda added a heap load more content and still have soo much space for modding

Correction no Fallout DLC has ever edited the in game map, however in Oblivion there was some rather excellent DLC that added places,characters and items to Cyrodil, including Mage Tower, Knights of the Nine and Fighters Stronghold

I think Broken Steel added many new locations to the map in the existing world?

I think the only actual map changes in terms of altering one area was the Rockland Car Tunnel in the southwest, and all they really did was add a door to the side of the wall (I'm excluding added set pieces, just new access points)

I'm going to assume they did that on purpose. What purpose, however, is a mystery to me.