The Circle line is a London Underground service in a spiralling shape, running from Hammersmith to Edgware Road and then looping once around central London back to Edgware Road. The railway is below ground in the central section and on the loop east of Paddingdon, and, unlike London's deep-level tube railways, the railway tunnels are just below the surface and of similar size to those on British main lines. Coloured yellow on the tube map, the 17-mile (27 km) line serves 36 stations, including most of London's main line railway termini. Most of the route and all of the stations are shared with the District, Hammersmith & City and Metropolitan lines.