Greening the cities - in pictures

The High Line was built in New York in the 1930s as part of a massive public-private infrastructure project called the West Side Improvement. It lifted freight traffic 30 feet in the air, removing dangerous trains from the streets of Manhattan's largest industrial district. Closed as a train route in 1980, it has now been transformed into a public park Photograph: James Leynse/Corbis

People walk along the High Line park, one of Manhattan's most popular tourist attractions,in the Meatpacking District Photograph: Spencer Platt/Getty Images

Letchworth Garden City, one of the first garden cities built in the UK Photograph: Alamy

Heygate estate in Elephant & Castle, south London, now being demolished Photograph: Alamy

Among the many speculative urban farming projects is MVRDV's "Pig City", a proposal for a vertical pig farm Photograph: MVRDV

The 606 in Chicago is a park and trail system, which includes the Bloomingdale Trail, five ground-level parks, and other amenities such as art installations, an observatory and skate park Photograph: The 606

The 606's old railway is being transformed into a 2.7-mile elevated trail spanning four neighbourhoods on Chicago’s north-west side Photograph: The 606

Visualisation of the Goods Line, Sydney, Australia. Aspect Studios and Choi Ropiha Fighera have been selected by the Sydney Harbour Foreshore Authority to design and deliver the park, which will be built on the 500m of industrial railway track that divides Ultimo from Haymarket Photograph: Sydney Harbour Foreshore Authority, ASPECT Studios and CHROFI

The Goods Line's walkway will sit four metres above street level and will improve access for pedestrians and cyclists from the Railway Square bus and train interchange into the south-west corner of Darling Harbour Photograph: Sydney Harbour Foreshore Authority, ASPECT Studios and CHROFI

A visualisation of the Garden Bridge in London, designed by Thomas Heatherwick to span the Thames from Temple to the South Bank Photograph: Arup

Winner in the High Line for London competition was Fletcher Priest Architects for a 'pop down' - a proposal to create a mushroom farm in tunnels beneath the city streets Photograph: Fletcher Priest Architects

Tsai Design's proposal for Cape Town, South Africa. It envisions transforming the city’s infamous unfinished highway overlooking the bustling downtown area into a public park, renewable energy generating station and a Museum of City Planning and Transportation Photograph: Tsai Design Studio

Unlike New York’s High Line, the road from the Unfinished Highway leads nowhere and is flanked by a network of roads that would make green space unrealistic. Instead Tsai Design recommends converting the disused space into a public viewing platform that overlooks Cape Town’s many outdoor performances Photograph: Tsai Design Studios

A little colony of Finnish-built wooden houses in the government district in Warsaw, Poland. Some have their windows boarded up as the city prepares to demolish them. The homes, erected as temporary housing in the destroyed capital just after World War II, have dwindled in number over the years from 90 to about 25. Now the surviving structures have become a point of contention between their inhabitants and a city government keen on tearing them down to make way for new developments Photograph: Czarek Sokolowski/AP