Ecumenopolis

An Ecumenopolis is the total urbanization of a planet. Such planets are worlds which are encompassed by one gigantic urban city which stretches across the entire surface. Ecumenopoli can be a singular 'level', or multi 'level', in which different layers of city are stacked on top of each other, forming multiple layers around the planet. While there are several hundred ecumenopolis planets, only about a dozen extend more than a couple levels deep. The ecumenopolis planet with the highest population and most levels is Kronos, capitol of the Federation. It has several 4,057 levels and is the most populated planet in the galaxy.