Planetopolis

Equal parts planet and metropolis, Planetopolis is a vast mega-city that spans the entire surface of a small planet. It serves as a central hub for the majority of commerce among the outer rim of the galaxy, with strong presences from many of the major sentient races.

Even the core of Planetopolis has no water (neither now nor in its past). All of Planetopolis' water is either synthesized/recycled or imported from off-world.

The core planet of Planetopolis is outrageously mineral-rich, having supplied most of the raw materials used to construct it and continuing to be useful for expansion and export.

All of it considered, Planetopolis is a medium-small planet. This still makes it an enormous city.

Literally speaking, the surface of Planetopolis has long since been entombed under a thick mantle of carbon and steel. Although originally lifeless, the core planetoid that serves as the center of Planetopolis remains incredibly resource-rich.

As it is truly an arcology/megastructure, Planetopolis does not have a naturally-occurring atmosphere or climate. However, the interior is devised in such a way that various sectors can be individually climate-controlled to suit the typical denizens.

There are a few large recreational modules among the spaces inside Planetopolis where artificially-created weather is able to happen, but generally speaking there is no weather on Planetopolis.

3.2 billion

Planetopolis has plenty of artificial satellites, but no naturally-occuring moons.