Green belt

The city of Ottawa, located in the middle of the map, is surrounded by the Ottawa Greenbelt

A green belt or greenbelt is a policy and land use designation used in land use planning to retain areas of largely undeveloped, wild, or agricultural land surrounding or neighbouring urban areas. Similar concepts are greenways or green wedges which have a linear character and may run through an urban area instead of around it. A green belt is basically an invisible line that goes around a certain area, stopping people from building there so that some of the wild and agricultural land can be saved.

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Green Belt Media

Green belt in Tehran, Iran
Adelaide Park Lands green belt around the city centre
Green belt at Thompson Park in Monroe Township, Middlesex County, New Jersey, U.S.
The green belt around the city of York, in England
Map of the Adelaide Park Lands
The central core of Ottawa, located in the middle of the map, is surrounded by the Ottawa Greenbelt
Photo aérienne de Rennes (Ille-et-Vilaine, France).
Green belts in England, with Metropolitan Green Belt outlined in red