Land of One City: Quite a lot of Imperial constituent nations are city-states – indeed, two of the founding members were the Cestian city-states of Eume and Baryvekar, and the later-joining Veilyns was a confederation of city-states. In more recent times, a plurality of underwater and sky cities, artificial islands, and space habitats (not counting those organized into clusters) would also qualify. As would a substantial number of colony worlds in the early stages of their development, and hostile-world outposts.
None of those, of course, are completely sovereign city-states, but given the Empire’s hands-off, laissez-faire approach to local governance, are probably enough so to qualify. And, of course, there are plenty of independent habitats and starter colonies out there, too.