London is a place.
London . London 's ancient core , the City of London , largely retains its 1.12 sqmi medieval boundaries . A report by PricewaterhouseCoopers published in November 2009 estimated that London had a city GDP measured in purchasing power parity of US$ 565 billion in 2008 , compared to US$ 564 billion for Paris , making them respectively the fifth - and sixth-largest in the world . London was the world 's most populous city from around 1831 to 1925 .