Central London consists of 3 cities - The City of London, The City of Westminster, and the City of Southwark.

The City of London is actually very small. It is often called "the Square Mile" which is a misnomer because it is neither square nor a square mile in area. The original city was bordered by the Tower of London in the south-east corner, the River Fleet on the west side and the city wall around the north side, between the Barbican and the Tower. Later, this was enlarged westward as far as Temple Bar close to the junction of Fleet Street and The Strand (in Westminster).

The City of Westminster begins at this point and stretches westward to Knightbridge and Bayswater, bounded on the south by the River Thames, and on the north by the far side of Regent's Park.

South of the Thames was, technically, the City of Southwark. The determination of what is a city or not is whether it has a Cathedral or a University. Southwark has a University and 2 Cathedrals - Southwark Cathedral (the mother church of the Anglican Diocese of Southwark), beside London Bridge, and St George's Cathedral (the cathedral of the Roman Catholic Archdiocese of Southwark), opposite the Imperial War Museum.

Southwark has traditionally not recognised as a city because the Puritans of the City of London looked down upon an area frequented by actors (disgusting people) and prostitutes (equally disgusting until needed by those same Puritans), even though the prostitution was organised by the Archbishop. Hence, it has traditionally been known as "the Borough".