Also on Phílae, most notably, are the several temporary floating cities likely to be present at any time, agglomerated together from a huge mass of houseboats and facboats and storeboats all lashed together into a giant city-like mass. (This is much more appropriate for Phílae than trying to build single large floating cities, since Phílae is a warm world without much land, and therefore remarkably prone to hypercanes. The ability to scatter and dodge them is very, very important.)
True artificial city-islands, on the other hand – of which the most famous is Calencine – were pioneered in Eliéra’s warm oceans as self-growing, self-repairing biotech constructs, with a customized biotech framework (including nutrient extraction and transport, and a bio-OTEC for power) supporting an island core of seacrete, island coral, and industrial bamboo.
But, in general, any world that has a hydrosphere and many that have an alkanosphere will have at least some of these.