What are the "specs" of the afterlife world?

Question

Regarding the afterlife world we see in the Angel Beats! anime, I have many questions, but I think we can pack all of them as "what are the specs of the afterlife world?":

• Are habitants limited to the school grounds? Can they, say, go somewhere really far away?
• Is this world based on an actual place in the living world? For instance, does this school actually exist somewhere?
• Do all individuals that die with regrets end up here? Surely millions of people die this way, and I'm pretty sure that we never see more than a few thousands.
• Are there other afterlife worlds? Or everyone ends up in the same place?

Answer 1

So for this bunch of questions I am going to use spoiler blocks as they are explained in the anime.

Limitations to school grounds:

If I recall correctly, Yuri mentioned something like "behind the school boundaries there is a large and wide area of nothing but grass" and that she tried to escape, but was not able to.

Based on any actual place:

In general, buildings are partly based on real buildings or generic. I would guess this school is a rag rug of multiple buildings mixed, excluding the underground facility of course ;)

Why not everyone / other afterlife worlds:

Well, everyone who dies with regrets seems to go to a certain place, where they can get over these regrets and live a new, untainted life. Also, most of the students are mere "filler material" / "background noise" to create a perfect environment. They were created by the "Programmer". This person wanted to create a perfect world for students to clear their regrets. Thus the school is only for students. This means a part of Japanese highschool students get to this special place created for them. For other people dying with regrets, there "must" be a different place to go.