Greenwich was a borough of London, in England. It was situated in the south-east region of the city and bordered the south bank of the River Thames.
Greenwich was the location of the Prime Meridian, the University of Greenwich, the Royal Observatory and the Federation Department of Temporal Investigations Headquarters. Greenwich Mean Timeis measured from there. (DS9 - Millennium novel: The War of the Prophets, DTI novel: Watching the Clock)