A city was a large collection of individuals.
The Doctor visited many cities during his various incarnations, including Byzantium, (PROSE: Byzantium!) New Byzantium, (PROSE: Shadowmind) New York City, (TV: The Angels Take Manhattan) Tenochtitlan, (PROSE: The Left-Handed Hummingbird) Valhalla, (AUDIO: Valhalla) and Venta Icenorum. (AUDIO: The Wrath of the Iceni)