The Desert Zone is, as the name implies, an arid region with plenty of inner conflict (caused by a lack of recovery from damaging past events) located on the Western part of Babel, separating most of Envylia and Wratharis from each other, as well as connecting from the East with Northern Pride, the Center of Babel. It is the home of the remainder of the Sephira, retaining many ancient ruins and relics of Sephiron.

See below where Desert Zone is:

Many important Units hail from here, especially the Protagonist of Part 2, Chapter 1: Kamui. The Desert Zone is also the primary location of the Chapter's events

For an expansive list of all the Units originated from the Desert Zone, see here.