London is the capital and most populous city of England, Great Britain, and the United Kingdom. Standing on the River Thames in the south eastern part of the island of Great Britain, London has been a major settlement for two millennia. It was founded by the Romans, who named it Londinium. London’s ancient core, the City of London, largely retains its 1.12-square-mile (2.9 km2) medieval boundaries and since at least the 19th century, the term London has also referred to the metropolis developed around this core. The bulk of this conurbation forms Greater London, a region of England governed by the Mayor of London and the London Assembly. The conurbation also covers two English counties: the small district of the City of London and the county of Greater London. The latter constitutes the vast majority of London, though historically it was split between Middlesex (a now abolished county), Essex, Surrey, Kent, and Hertfordshire. However many residents of districts that were historically part of one of these counties continue to consider said districts as not being part of London.
London’s vast urban area is often described using a set of district names, such as Bloomsbury, Mayfair, Wembley and Whitechapel. These are either informal designations, reflect the names of villages that have been absorbed by sprawl, or are superseded administrative units such as parishes or former boroughs.
source: Wikipedia – London