Greater London includes the most closely associated parts of the Greater London Urban Area and their historic buffers and includes, in five boroughs, significant parts of the Metropolitan Green Belt which protects designated greenfield land in a similar way to the city's parks. The closest and furthest boundaries are with Essex to the northeast between Sewardstonebury next to Epping Forest and Chingford and with the Mar Dyke between Bulphan and North Ockendon. Greater London is also bounded by Hertfordshire to the north, Berkshire and Buckinghamshire to the west, Kent to the southeast and Surrey to the south and southwest. The highest point is Westerham Heights, in the North Downs and on the boundary with Kent, at 245 metres (804 ft).