Each Map happens in one of the characters home lands.

[Guest gameguy]

So I found something very interesting about all the zombie maps, each one happens in one of the characters countries.

Natch Der Untoten, Verruckt, Der Riese and Kino der toten are all in Germany, Richtofen's country.

Shi No Numa and Shangri-la are in Japan, or at least Asia for Takeo.

Ascension and Call of the Dead are in Russia for Nikolai.

EDIT-

But only one map happens in America for Tank, Five. Now looking at all characters except for Richtofen who I kind of consider as the main character, they each have two maps but Dempsey. Now we all know Area 51 is in America and I think it's been confirmed you will go there on moon, so moon will become Dempsey's second map.

[Guest Juice503]

There has been a lot of talk about this throughout the life of the games, and it could either be that the designers meant for this to happen, or it could just be that they wanted diversity between locations, and the only places they would have the maps are where warring countries are.

[Guest InfestLithium]

There has been a lot of talk about this throughout the life of the games, and it could either be that the designers meant for this to happen, or it could just be that they wanted diversity between locations, and the only places they would have the maps are where warring countries are.

I'm going to concur with that. Keep in mind that they have to make the settings related to Cold War (even if you are following the Zombies storyline).

Dempsey has Five, if going along with your theory.

[Guest gameguy]

Oh, yeah I knew I was forgetting a map but I couldn't think of it, I'm gonna edit that in.