The City of London is a geographically small city within Greater London. The City’s boundaries have remained almost constant since the Middle Ages, and hence it is now only a tiny part of the much larger London metropolis. It is often referred to as the City or the Square Mile, as it is just over one square mile (1.12 mile² / 2.90 km²) in area. The City is today a major business and financial centre, ranking on a par with New York City as the leading centre of global finance; in the 19th Century, the City served as the world's primary business centre. The City has a resident population of under 10,000, whilst it employs 340,000 professional workers, mainly in the financial sector, making the area's transport system extremely busy during peak times. sourced from wikipedia