Kentucky; Seattle, Washington; Knoxville, Tennessee; and San Jose, California. Urban growth boundaries also exist in Miami-Dade County, Florida and the Minneapolis–Saint Paul metropolitan area of Minnesota. In Miami-Dade, it is referred to as the Urban Development Boundary (UDB), and is generally to protect from continued sprawl into and drainage of the Everglades. Portland, Oregon is required to have an urban growth boundary which contains at least of vacant land. Urban growth boundaries have come under an increasing amount of scrutiny in the past 10 years as housing prices have substantially risen, especially on the West Coast of the U.S. By limiting the supply of developable land, critics argue, UGBs increase the price of existing developable and already-developed land. As a result, they theorize, housing on that land becomes more expensive. In Portland, Oregon, for example, the housing boom of the previous four years drove the growth-management authority to substantially increase the UGB in 2004. While some point to affordability for this action, in reality it was in response to Oregon State law. By law, Metro, the regional government, is required to maintain a 20-year supply of land within the boundary. Even with the addition of several thousand acres (several km²) housing prices continued to rise at record-matching paces. Supporters of UGBs point out that Portland's housing market is still more affordable than other West Coast cities, and housing prices have increased across the country. See also Community separator Green belt Land use planning Prime farmland Tree Urban open space Urban rural fringe Urban sprawl References External links Metro: Urban growth boundary: information on the Portland, Oregon-area boundary Chronology of land use legislation in Oregon, 1969–present Urban planning Town and country planning in the United Kingdom Local government in the United Kingdom Housing in the United Kingdom Urbanization