Ecumenopolis

A depiction of Trantor, a fictional ecumenopolis from Isaac Asimov's Galactic Empire

Ecumenopolis (from Ancient Greek οἰκουμένη (oikouménē) 'the inhabited world' and πόλις (pólis) 'city'; lit.'world city'; pl. ecumenopolises or ecumenopoleis) is the hypothetical concept of a planetwide city.