Zoning is a North American term for a system of land-use regulation. The word is derived from the practice of designating permitted uses of land based on mapped zones which separate one part of a community from another.

Zoning regulations fall under the police power rights governments may exercise over real property. Theoretically, its primary purpose is to segregate uses that are thought to be incompatible; in practice, zoning is used as a permitting system to prevent new development from harming existing residents or businesses. Zoning is commonly controlled by local governments such as counties or municipalities.

Zoning commonly includes regulation of the kinds of activities which will be acceptable on particular lots (such as open space, residential, agricultural, commercial or industrial), the densities at which those activities can be performed (from low-density housing such as single family homes to high-density such as high-rise apartment buildings), the height of buildings, the amount of space structures may occupy, the location of a building on the lot (setbacks), the proportions of the types of space on a lot (for example, how much landscaped space and how much paved space), and how much parking must be provided.

Origins and history of zoning

New York City adopted the first zoning regulations to apply city-wide in 1916 as a reaction to construction of The Equitable Building (which still stands at 120 Broadway). The building towered over the neighboring residences and cast long shadows that diminished the quality of life for the people in the affected area. These laws, written by a commission headed by Edward Basset and signed by Mayor John Purroy Mitchel, became the blueprint for the rest of the country; partly because Edward Basset headed the group of planning lawyers which wrote The Standard State Zoning Enabling Act that was accepted almost without change by most states. The effect of these zoning regulations on the shape of skyscrapers was famously illustrated by architect and illustrator Hugh Ferriss.

By the late 1920s most of the nation had developed a set of zoning regulations that met the needs of the locality. New York City went on to develop ever more complex set of zoning regulations, including floor-area ratio regulations, air rights and others according to the density-specific needs of the neighborhoods.

Among large cities in the United States, Houston, Texas is unique in having no zoning ordinance. Houston voters have rejected efforts to implement zoning in 1948, 1962 and 1993. Thus Houston continues to be the largest city in the U.S. with no zoning.

Types of Zoning

Zoning codes have evolved over the years as urban planning theory has changed, legal constraints have fluctuated, and political priorities have shifted. The various approaches to zoning can be divided into four broad categories: Euclidean, Performance, Incentive, and Design-based.

Euclidean zoning

Named for the type of zoning code adopted in the town of Euclid, Ohio, Euclidean zoning codes are by far the most prevalent in the United States, used extensively in small towns and large cities alike. Also known as "Building Block" zoning, Euclidean zoning is characterized by the segregation of land uses into specified geographic districts and dimensional standards stipulating limitations on the magnitude of development activity that is allowed to take place on lots within each type of district. Typical types of land-use districts in Euclidean zoning are: residential (single-family), residential (multi-family), commercial, and industrial. Uses within each district are usually heavily prescribed to exclude other types of uses (residential districts typically disallow commercial or industrial uses). Some "accessory" or "conditional" uses may be allowed in order to accommodate the needs of the primary uses. Dimensional standards apply to any structures built on lots within each zoning district, and typically take the form of setbacks, height limits, minimum lot sizes, lot coverage limits, and other limitations on the building envelope.

The zoning ordinance of Euclid, Ohio was challenged in court by a local land owner on the basis that restricting use of property violated the 14th Amendment of the U.S. Constitution. Though initially ruled unconstitutional by lower courts, the zoning ordinance was upheld by the U.S. Supreme Court in Village of Euclid v. Ambler Realty Co. (1926). See below for more information.

Euclidean zoning is preferred by many municipalities due to its relative effectiveness, ease of implementation (one set of explicit, prescriptive rules), long-established legal precedent, and familiarity to planners and design professionals. Euclidean zoning has received heavy criticism, however, for its lack of flexibility and institutionalization of now-outdated planning theory.

Performance zoning

Performance zoning uses performance-based or goal-oriented criteria to establish review parameters for proposed development projects in any area of a municipality. Performance zoning often utilizes a "points-based" system whereby a property developer can apply credits toward meeting established zoning goals through selecting from a 'menu' of compliance options (some examples include: mitigation of environmental impacts, providing public amenities, building affordable housing units, etc.). Additional discretionary criteria may also be established as part of the review process.

Performance zoning is known for its high level of flexibility. However, performance zoning can be extremely difficult to implement and may require a high level of discretionary activity on the part of the supervising authority. For this reason, performance zoning has not been widely adopted and is usually limited to specific categories within a broader prescriptive code when found.

Incentive zoning

First implemented in Chicago and New York City, incentive zoning is intended to provide a reward-based system to encourage development that meets established urban development goals. Typically, a base level of prescriptive limitations on development will be established and an extensive list of incentive criteria will be established for developers to adopt or not at their discretion. A reward scale connected to the incentive criteria provides an enticement for developers to incorporate the desired development criteria into their projects. Common examples include FAR (floor-area-ratio) bonuses for affordable housing provided on-site and height limit bonuses for the inclusion of public amenities on-site. Incentive zoning has become more common throughout the United States during the last 20 years.

Incentive zoning allows for a high degree of flexibility, but can be complex to administer. The more a proposed development takes advantage of incentive criteria, the more closely it has to be reviewed on a discretionary basis. The initial creation of the incentive structure in order to best serve planning priorities can also be challenging and often requires extensive ongoing revision to maintain balance between incentive magnitude and value given to developers.

Design-based zoning

Design-based zoning relies on inter-related schedules of rules to be applied to development sites according to both prescriptive and discretionary criteria. These criteria are typically dependent on lot size, location, proximity, and other various site- and use-specific characteristics.

Design-based codes offer considerably more flexibility than Euclidean codes, but can be very complex to create and administer. Design-based codes have not been widely adopted in the United States and are often criticised as overly-constraining and difficult to interpret where they have been used.

One example of a recently adopted code with design-based features is the Land Development Code adopted by Louisville, Kentucky in 2003. This zoning code created "form districts" for Louisville Metro. Each form district was intended to recognize that some areas of the city were suburban in nature, and some urban. Building setbacks, heights and design features vary according to the form district. As an example, in a "traditional neighborhood" form district, a maximum setback might be 15 feet from the property line, while in a suburban "neighborhood" there might be no maximum setback at all.