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
Central line (London Underground) it is the only Tube line running east–west through the central core of London, running under Oxford Street and the financial centre of the City of London. Crossrail, due to begin most of its core operation in autumn 2019 with full service by the end of 2019, will provide interchange with the Central line at Stratford, , , and Ealing Broadway, relieving overcrowding in these areas. The Central London Railway (CLR) was given permission in 1891 for a tube line between Shepherd's Bush and a station at Cornhill, and the following year an extension to Liverpool Street was authorised, with