Tycho City is located on Earth's Moon and probably part of the Lunar colonies. The city has self-contained atmosphere and artificial gravity (presumably to Earth standard).
Cadet Dorian Collins was from Tycho City. (DS9: "Valiant")
By 2373, it was large enough to be seen from Earth at daytime, since Commander William Riker missed the familiar sight of the city, while looking at the Moon during his mission to the year 2063. (Star Trek: First Contact)
- Named either after the Danish astronomer Tycho Brahe of the 16th century, or the lunar crater Tycho.
Background
Tycho City has a long and venerable history in science fiction film and television. It is the location of the "magnetic anomaly" (TMA-1) excavation site on the moon in Stanley Kubrick's seminal 1968 sci-fi classic 2001: A Space Odyssey. There was a small, perhaps temporary, base at Tycho. Kubrick's depiction of the main Clavius Base was the inspiration for Moonbase Alpha of TV's Space: 1999.
There is also a Tycho City in the roleplaying game Gamma World. It is almost de rigeur for any science fiction show such as Star Trek to include the most "famous" fictional settlement on Earth's moon.