ゾーニング (都市計画)
概要
どの区域にあるかによって、そこにおける特定の開発行為に対して開発許可が下りるか否かが決まる。ゾーニングは、様々な形で、もっぱら特定の土地利用のみを認めることもあれば、土地利用に条件を付けていく場合もある。場合によっては、土地の面積や形状、さらに建物の形や大きさに条件を付けることもある。こうした指針は、都市の成長と発展を誘導する目的で設定される。
然るべき当局によって分割された土地では、区域によって様々な土地利用が許可される。このため、多くの先進諸国において、ゾーニングは、地方政府が都市計画の手段として、土地利用計画の技法を用いている。「ゾーニング (zoning)」という表現は、土地利用、形状、開発計画やその適合性などによって、地図上に区域/ゾーン (zone) を線引きしていく行為に由来している。法律上、ゾーニング計画は、然るべき手続きを経て条例として発効する。一般的なゾーイニング条例などは、その多くが子供たちが通う学校周囲に、大人向けの各商業施設（酒販売、ギャンブル、性的娯楽など）の設置を制限するものとして知られている。カナダやドイツなど、一部の国々においては、ゾーニング計画は、より上位の地方政府（地方、州など）による計画や政策に従わなければならない。
ゾーニングの類型には非常に大きな多様性があり、建物の形状や街路と建物の位置関係に規制に焦点を当てた形態規制条例と称されるものもあれば、土地利用の区分を重視する利用規制や、これらを折衷したものもある。同様に、特定の区域の利用目的を決めてしまうという都市計画上の手法も、古代以来数多くの都市で採用されてきた。
人口密度規制の経済的説明
Rothwell and Massey suggests homeowners and business interests are the two key players in density regulations that emerge from a political economy. They propose that in older states where rural jurisdictions are primarily composed of homeowners, it is the narrow interests of homeowners to block development because tax rates are lower in rural areas, and taxation is more likely to fall on the median homeowner. Business interests are unable to counteract the homeowners' interests in rural areas because business interests are weaker and business ownership is rarely controlled by people living outside the community. This translates into rural communities that have a tendency to resist development by using density regulations to make business opportunities less attractive.
使い捨てゾーニング
Single-use zoning,  also known as Euclidean zoning, is a tool of urban planning that controls land uses in a city. The earliest forms of single-use zoning were practiced in New York city in the early 1900s, to guide its rapid population growth from immigration. Land uses were divided into residential, commercial and industrial areas, now referred to as zones or zoning districts in cities. Single-use zoning became known as Euclidean zoning because of a court case in Euclid, Ohio, which established its constitutionality, Village of Euclid, Ohio v. Ambler Realty Co. 272 U.S. 365 (1926).
Euclidean zoning has been the dominant system of zoning in much of North America since its first implementation. The predictable model for dividing land use patterns generated by the Euclidean system have been charged by many commentators as playing a direct role in a number of problems in land use planning evident in the United States and elsewhere. Single-use zoning is a basic model that has not evolved to create appropriate solutions for the increasing complexity of social, political and environmental challenges in cities.
Problems affiliated with Euclidean-style zoning policy include urban sprawl, urban decay, environmental pollution, racial and socioeconomic segregation, negative economic impacts and an overall reduced quality of life. Land use regulations associated with a high separation of land uses have also been criticized as being fraught with legal obstacles to rehabilitating neighbourhoods affected by the aforementioned problems  (such efforts are often referred to as urban rehabilitation or urban renewal).
Euclidean zoning represents a functionalist way of thinking that uses mechanistic principles to conceive of the city as a fixed machine. This conception is in opposition to the view of the city as a continually evolving organism or living system, as first espoused by the German urbanist Hans Reichow.