There are regions of incomplete and half-finished demi-planes, the so-called 'inchoate realms,' that were for some reason abandoned by their projectors-dangerous places for even powerful Daedra to visit, as it's easy to become discorporated in a Roamver ambush, or by getting caught up in a realm-rip. In my experience, such 'collective realms' tend to be rather mundane and uninteresting, lacking the distinctive qualities of the more personal Oblivion planes. There are physical realms, such as Infernace, home of the flame atronachs, that exist as collective extensions of their numerous, less-powerful inhabitants.
Exceptional realms deviate from this norm in several ways. Indeed, reality as personal manifestation is the norm in all the highly-organized realms I have visited. Lord Fa-Nuit-Hen says, “To answer your questions, Spellwright, I shall go from the specific to the general! In common with the greater Princes, my realm of Maelstrom and myself are indistinguishable-my pocket reality is a projection of my mind, nature, and will.
