The concept of a green belt surrounding cities goes back a long way.
According to Arabic scholars, the Prophet Mohammed established a green belt around the city of Medina by prohibiting the removal of trees in a 20km strip around the city.
In the 20th century, the United Kingdom's government, under pressure from countryside campaigners, introduced green belts as a planning tool.
The first was created around the London metropolitan area in 1938 and then the concept was rolled out across England as a whole by a government circular in 1955.
Over the years, hundreds of cities around the globe have employed similar urban planning rules.
In Canada, examples include the Ottawa Greenbelt and the Golden Horseshoe Greenbelt in Ontario.
In other countries, urban planning has sought to preserve open spaces in similar manners.
In the Netherlands, which is under pressure to use its limited land mass for housing, the city authorities protect a groene hart - a green heart surrounded by the cities of Rotterdam, The Hague, Amsterdam, Utrecht and Leiden Haarlem.
New Zealand boasts one of the world's oldest green belts, implemented during the gold rush years of the 1860s.
The city of Melbourne in Australia is protected by a "green wedge".
In America, states such as Oregon, Washington and Tennessee require cities to establish urban growth boundaries. And in Brazil, the city of São Paulo has been surrounded by the city's Green Belt Biosphere Reserve since 1994.
In recent years, the concept has evolved to encompass various urban green spaces such as parks.
In 1994, the Swedish government created Ekoparken, a series of national city parks through an act of parliament, in Stockholm and the nearby municipality of Solna.