London Underground ticketing destinations and most interchange stations are in zone 1, meaning that most journeys over similar distances will cost the same. A few stations in the north east of the network, on the Central line, outside Greater London (in the Epping Forest district) are in zones 4, 5 and 6. In the north west of the network, on the Metropolitan line, zones 7, 8 and 9 (formerly A - D) cover stations outside Greater London including Amersham and Chesham in the Chiltern district of Buckinghamshire. Unlike the lower numbered zones, these ancillary areas do not encircle the capital. Some stations are
Greater London boundary with Kent, at 245 metres (804 ft). Central government has implemented small boundary changes. The greatest were the 1969 transfers of Farleigh to Surrey and Knockholt to Kent. Others have included exchange of two Thames islands with Surrey and adjustments during the 1990s to parts of the boundaries of three boroughs near the M25. The only part of Greater London outside the motorway is North Ockendon, the furthest land unit from its centre. The majority of Greater London forms the London low emission zone. The London postal district does not cover all of Greater London. The Mayor of London