Greater London is often referred to as "the City" or "the Square Mile" and it forms the main financial district. Archaically, the urbanised area of London was known as the Metropolis. In common usage, the terms "London" and "Greater London" are usually used interchangeably. Greater London is officially divided for some purposes, with varying definitions, into Inner London and Outer London. For some strategic planning purposes it is divided into five sub-regions. Greater London is under the strategic local governance of the Greater London Authority (GLA). It consists of an elected assembly, the London Assembly, and an executive head, the Mayor of
City of London known as 'Barts'. Founded in 1123, it is located at Smithfield, and is undergoing a long-awaited regeneration after doubts as to its continuing use during the 1990s. The City is the third largest UK patron of the arts. It oversees the Barbican Centre and subsidises several important performing arts companies. The London Port Health Authority, which is the responsibility of the Corporation, is responsible for all port health functions on the tidal part of the Thames, including various seaports and London City Airport. The Corporation oversees the running of the Bridge House Trust, which maintains London Bridge, Blackfriars Bridge, Southwark