The etymology of London is uncertain, but is known to be an ancient name. The concept of East London as a distinct area is a relatively recent innovation. John Strype's map of 1720 describes London as consisting of four parts: The City of London, Westminster, Southwark and "That Part Beyond the Tower". From the late 19th century the term East End of London was used to describe areas immediately adjacent to the City in the Tower division of Middlesex. Charles Booth in 1889 defined East London as the County of London between the City and the River Lea. In 1902 he now considered this area to be the "true East End", and his attention had been drawn eastward over the Lea into the Borough of West Ham, which was then outside London, and geographically in Essex, but under the authority of neither; in 1857 Charles Dickens termed it "London-over-the-Border". Walter Besant described East London as an area north of the Thames and east of the City that stretched as far as Chingford and Epping Forest, which was similar to the definition used by Robert Sinclair in 1950 that stretched east to include Barking and Dagenham. This broadly matched the Metropolitan Police District east of the city and north of the Thames at that time, and now corresponds to the boroughs of Barking and Dagenham, Hackney, Havering, Newham, Redbridge, Tower Hamlets and Waltham Forest in Greater London.