I have only explored the central to eastern section of the map so far. Can you go right up to the edges of the map shown on the pip-boy or are there mountains and stuff in the way before you get there?
 Just trying to gauge the actual size of the area I have to explore.

Yes, there are invisible walls. Don't think you can actually reach any corners of the map really.

Yup, sometimes you can see a clear path to, say, a certain dam but some invisible wall is holding you back. It's annoying obviously but you can manage. It isn't a boxed area, per se, as most of these, at least the ones that I've come across are either unclimbable mountains or walls that wrap aroumd certain formations that are clearly traversable.

I turned off clipping for shits and giggles to go past the map boundaries and to the edge. Took some time tho. But there you will truly understand the meaning of "wasteland"

from what I've explored the north west corner has a road that ends with a big puddle of radioactive water littered with cars and cannot be passed. The southwest corner has the NCR base and a fence I can't open. The south east is just Legion territory and there's only the fort that can be accessed. (I cant get to that side of the Colorado even through lake Mead.)
 
anyone else explore more? I would appreciate any help.