The Norwood Ridge is a rectangular upland which occupies the geographical centre of south London, centred south of London Bridge. Beneath its topsoil it is a ridge of London Clay that is capped on all sides (including as isolated knolls in the north) with remaining natural gravel deposits mixed with some sandy soil, which in the South Thames basin is a material known as the Claygate Beds. Extent and components The area is rectangular, measuring broad. Its longest side is if measured from central Brockley around which are three related knolls including Rye Hill, Nunhead or less if the start-point of the ridge is taken as One Tree Hill, Honor Oak. The upland is visible on terrain maps as three main parts of different elevation. The high, eastern ridge (Sydenham Hill Ridge) runs from One Tree Hill SSE forming: the high western halves of Honor Oak and Forest Hill, then Upper Sydenham, the east of Gipsy Hill and Crystal Palace (which has, since the station of that name was built, among many residents replaced the Sydenham Hill and Anerley Hill names, except chiefly for the road Sydenham Hill which sits on the ridge), then Upper Norwood, then South Norwood Hill then the north-east of Thornton Heath and far north of Selhurst, in particular Grangewood Park. Upon the ridge is the Crystal Palace transmitting station, founded in 1933, the main television transmitter for the London area, and also the Croydon transmitting station. The ridge is above and from a few raised west-facing places the western ridge can be seen, beyond which is similar height Wimbledon Common. The north has very narrow peaks which allow views of the tall buildings of Central London, but the ridge's eastern slope widely commands unobstructed views over Bromley and Addiscombe to the rises of Chislehurst as well as higher Kent parts of the North Downs. Nineteen of its access or approaching roads could be mistaken as forming separate structures, the greatest of which is the broad south slope leading west, Beulah Hill:- Beulah Hill and Upper Beulah Hill, off of which are the following approaches: Spa Hill Biggin Hill (not to be confused with Biggin Hill further south at the edge of Greater London. Norbury Hill Convent Hill Gibson's Hill Grange Hill Sylvan Hill and Beaulieu Heights Highfield Hill Fox Hill Westow Hill Anerley Hill Central Hill Salters Hill Westwood Hill Round Hill Derby Hill Manor