OK, found a good reference. A Habble is indeed a political distinction in the sense that it has a semi-autonomous government, and representation on the Spire Council and whatnot, but they are also geographic. Each Habble is also a single layer of the Epire. Each layer is a circular slice, with a square contained within. Each square is where the living space is, while the leftover bits on the cardinal directions contain the tunnels and support machinery that makes the whole spire operate and support it's inhabitants. There is also mention of a central spiraling stairs/ramp/walkway that each habble has rights an allotted percentage of the space/traffic, and that they charge a premium for any who use it.