The central Demonic Plane is large, but limited. When the Demons were first pushed into it, there was more than enough space.

That time has long since passed.

The central Demonic Plane has been filled to the brim with the organic dwellings. Smaller realms have been attached to the larger one, each controlled by a Demonic Master. The space in these are jealously guarded.

Within the central Demonic Plane there has evolved a hierarchy of desirability. Near the top the air is cleaner, the buildings newer, and only Demons of note can live there safely.

The very bottom is a place of sludge, waste, and death. It is highly dangerous and prone to spawning magical creatures of very low intelligence.

Every tier above that is more maintained, with more enforced order.

Still, the lower planes have a certain level of popularity with Demons, as long as they are capable of defending themselves, and the things they care about.

(there follows a rough diagram of the planes, in cross section form)

-Restricted information, available only to the Angels and the highest priests