An ecumenopolis is a planet or moon whose entire surface is covered by cityscape. The word is derived from the Greek οικουμένη (oikoumene), meaning "world", and πόλις (polis) meaning "city"; thus a "world-city" (pl. ecumenopolises or ecumenopoleis). Ancient works of science fiction on most worlds have depicted ecumenopolises.
Over time, a species may end up transforming their homeworld into an ecumenopolis. This is not always the case; sometimes urbanization is restricted for the sake of preserving natural areas. Planets that do undergo complete urbanization often transport the remaining surface wildlife to wildlife sanctuary planets or facilities, or simply enclose such areas in climate-controlled domes and build over them. In more extreme cases, the oceans themselves will be built over or even drained entirely.
According to most academics, the landmasses of a planet or moon must be at least 90% covered by cities in order to class as an ecumenopolis, although that definition is challenged by critics who say that an ocean world with a single urbanized island would technically fall into that category.
The standard ecumenopolis will often feature gargantuan facilities (which can be dozens of miles in width) devoted entirely to food production, water storage and purification, and waste treatment. Massive food shipments from outside sources are also common.
Waste heat is handled by various means, often by the implementation of heat dissipators in each structure. Other ecumenopolises may resort to using massive and powerful refrigeration towers, as seen on Riesel.
The buildings themselves are commonly constructed with lightweight and durable metamaterials, some of which naturally negate gravity. Gravity repellers are also employed for stability, acting similar to vernier thrusters or invisible guy-wires to prevent the buildings from swaying excessively.
Occurrence in the galaxy
Urban worlds are not particularly uncommon and usually occur along major trade routes. There are thousands of lesser variants (i.e. most of the cityscape is below a mile in height), and a few hundred whose towers stretch up beyond a mile.