A greenbelt is an urban planning concept. It's aim is to retain undeveloped, wild, or agricultural land around an urban area. Along these lines, Ann Arbor, Michigan is acquiring conservation easements on agricultural land around the city. While the city's initial plan did not include the participation of surrounding townships, at least four townships have participated directly or have initiated their own efforts to protect agricultural land surrounding the city. (Source: http://en.wikipedia.org/wiki/Green_belt)