Glossary

The following glossary should be used to interpret terms used on this website, in our data collection, and in our products. We believe that a consistent use of terms can bring some order to a highly fragmented regulatory landscape.

Geographic Units

These are the geographic units that organize our mapping schema.

  • A jurisdiction is a type of local government entity—such as a city, town, village, or county—or a nongovernmental entity, such as a homeowners’ association, that has been granted the power by state legislatures to exercise zoning authority.

  • A county is a governmental entity defined as a county by the Census, including “county equivalents”—such as Louisiana’s parishes or Connecticut’s councils of governments (COGs). In many states, counties are vested with zoning authority, and we count them as jurisdictions. In other states, they are not jurisdictions in NZA parlance, but they may contain jurisdictions.

  • A Core-Based Statistical Area (CBSA) is a metropolitan or micropolitan statistical area, defined by the U.S. Office of Management and Budget and consisting of a central core with a significant population, along with surrounding communities that are strongly connected to the core through economic and social ties. The NZA uses current delineations for these areas, which took effect in July 2023.

  • A state refers to any of the 50 U.S. states, as well as the District of Columbia.  

Zoning Components

The following core components of zoning codes are foundational to our data collection and analysis.

  • A zoning code is a law, adopted by a jurisdiction, which governs how land within the jurisdiction’s boundaries may be used and developed. Each zoning code consists of two components: the zoning text, which sets forth the rules, and the zoning map, which depicts how those rules apply geographically.

  • A zoning text is a document setting out the rules governing how land may be used and developed within each zoning district of a jurisdiction. For each zoning district, the text typically establishes which uses—such as residential, commercial, or industrial—are permitted or prohibited, and sets standards for buildings (e.g., height limits) and lot characteristics (e.g., setbacks, parking requirements). While zoning texts are dominated by words, they also contain tables, charts, and diagrams.

  • A zoning map is the visual counterpart to the zoning text. It depicts the geographic boundaries of each mapped zoning district (including base and any overlay districts), typically using color-coding or labels to differentiate between districts. Jurisdictions offer zoning maps in static form (e.g., PDF, graphic file, or even hand drawing), a digital map, or both.

  • A zoning district (or zone, or district) is a distinctly regulated area, with rules laid out in the zoning text. Districts can be base or overlay districts. Districts can be mapped or, if only mentioned in the zoning text, unmapped. If a district is mapped but not mentioned in the text, NZA characterizes it as extinct.

  • A base zoning district is an ordinary zoning district insofar as each parcel of land subject to zoning must be assigned a base district. It is distinct from an overlay zoning district, which is mapped on top of a base district for the purpose of modifying or supplementing base district regulations.

  • An overlay zoning district, or overlay, is mapped on top of a base district to modify or supersede certain base district regulations. In some cases, overlays may overlap with one another. Overlays are typically used to address specific issues or policy goals, such as protecting environmentally sensitive areas (such as wetlands, floodplains, habitats) or preserving historic and cultural resources.

Types of Zoning Districts

We classify zoning districts, including both base and overlay districts, into three primary categories. (In addition, we note in our files some overlays that do not affect residential uses.)

  • Primarily Residential zoning districts allow housing as the main (principal) use. Their core purpose is to regulate and encourage residential development. They may also allow a limited set of nonresidential or secondary activities historically associated with residential neighborhoods, such as places of worship, schools, parks, or home-based businesses.

  • Mixed with Residential zoning districts allow housing as a principal use alongside a wide range of nonresidential uses. Residential development may take the form of stand-alone housing or may be integrated with commercial or institutional uses (such as retail on the ground floor with residential above). Permitted nonresidential activities often include retail shops, restaurants, offices, medical facilities, and light industrial uses.

  • Nonresidential zoning districts prohibit housing as a principal use entirely. These districts permit, for example: heavy industrial uses, office parks, institutional and governmental areas, public utilities and airports, cemeteries, or open space and recreation.

Types of Residential Uses

We use the following terms when classifying residential uses.

  • One-family housing, or single-family housing, refers to a single dwelling unit built as a principal use on an individual lot. Single-family housing can be detached, semi-detached, or attached (like a townhome). 

  • Two-family housing refers to two dwelling units built as a principal use on an individual lot. Two-family housing, sometimes called duplexes, can appear as two units in the same building, two buildings attached, or two buildings detached. Where two dwelling units are allowed but one must be smaller than the other, we classify the smaller unit as an accessory dwelling unit, and the larger unit as 1-family housing.

  • Three-family housing refers to three dwelling units built as a principal use on an individual lot. Three-family housing, sometimes called triplexes, can appear as three units in the same building, three buildings attached, or three buildings detached.

  • Four-or-more-family housing refers to four or more dwelling units built as a principal use on an individual lot. These building types, often referred to as multi-family housing, apartments, or quadplexes (if four units exactly), are designed to accommodate multiple households within a single building, or can appear as a group of interconnected structures, like condominiums, townhouses, or large apartment blocks.

  • Accessory dwelling units (ADUs), also known as granny flats, in-law suites, or casitas, are secondary residential units located on the same lot as a principal dwelling unit or a nonresidential use. They may be built within the main structure, attached to it, or separate from the primary structure, but they are always smaller than the primary unit. Where two dwelling units are allowed on a single lot without regard to size, we classify them as 2-family housing. Zoning codes sometimes impose additional restrictions on ADUs, including public hearing and occupancy requirements.

  • Planned residential developments (PRDs), also known as planned unit developments or master plan communities, include multiple dwelling units built pursuant to an approved master plan. This plan often establishes the placement and size of structures, open space requirements, and design guidelines.. The plan may permit dwelling units in multiple buildings, on smaller subdivided lots, or within a single parcel. The NZA defines PRDs to include mobile and manufactured home parks.

  • Elderly housing refers to housing that will be occupied by people over a certain age, usually around retirement age.

  • Affordable housing refers to any housing that must be designated affordable in some way, such as all or some units being subject to rent caps, deed restrictions, set-asides of units, payments, or occupancy limitations. 

Regulations on Residential Uses

We classify the permitting process for land uses into one of three categories.

  • Allowed means a proposed use or development is permitted subject to administrative review by staff or a zoning authority, in some cases after satisfaction of specified conditions. This category is synonymous with “as of right” or “by right” zoning. 

  • Public Hearing means a proposed use or development is permitted subject to a formal meeting in which members of the public may provide input. The meeting might be convened by a city council, a planning commission, a zoning commission, or any other zoning authority. 

  • Prohibited means that a proposed use or development is either expressly prohibited or not explicitly mentioned.

Regulations on Buildings

These terms refer to the different regulatory strategies used to regulate buildings.

  • A building’s maximum height is the highest allowable distance between the ground plane and the top of the building, defined in the zoning text in terms of number of stories, linear feet, or both. 

  • A floor-to-area ratio (FAR) is calculated by dividing the total floor area of all buildings on a lot by the total area of the lot. In zoning texts, FAR is typically expressed as a decimal or percentage. For example: On a lot of 10,000 square feet, a FAR of 0.5 (50%) means the building’s maximum floor area is 5,000 square feet. In practice, this means a building could be one story covering 5,000 square feet, or two stories of 2,500 square feet each.

  • A minimum unit size is the smallest allowable floor area for dwelling units. It is typically defined in the zoning text as a number in square feet. Minimum unit sizes may vary by the number of bedrooms. For example: A zoning text might mandate that a studio apartment be at least 400 square feet, while a 2-bedroom dwelling unit be at least 800 square feet.

  • The maximum number of bedrooms is a cap on the number of bedrooms per dwelling unit. 

  • The maximum number of units is a cap on the number of units allowed to be developed. We track this for 4+-family dwellings and in planned residential developments.

Regulations on Lots

These terms refer to the different regulatory strategies used to regulate lots.

  • A minimum lot size requirement specifies the smallest allowable parcel of land that can be developed for a given housing type. The lot size is typically defined in the zoning text as a number in square feet or acres. Sometimes, the lot size varies, including, for example, on whether the housing is affordable housing or market-rate housing. 

  • A maximum density requirement caps the number of dwelling units or buildings allowed relative a given land area. A zoning text typically defines maximum density as a ratio of units to acres: the higher the number, the greater the permitted density. 

  • A parking requirement is a common zoning regulation that dictates the number of parking spaces a property must provide based on the size and types of its residential units. Sometimes, the parking mandate varies, including, for example, by the number of bedrooms in a dwelling unit.  

  • A sewer and/or water connectivity requirement mandates that new developments be connected to public sewer and/or water systems. These requirements apply to publicly provided infrastructure and do not include private systems such as wells or cisterns.

  • A transit connectivity requirement ensures that new developments are located near (typically within a half mile of) and well-integrated with public transportation systems. 

  • A setback requirement designates the minimum distance between a parcel’s property lines and where a building or structure is permitted to be built. A zoning text typically defines minimum setbacks as a number of feet or percentage of lot depth, and may differentiate between front, rear, side, corner, and interior setbacks, or specify contextual rules for setbacks depending on the shape of the lot, such as a corner lot.  

  • A maximum lot coverage requirement is the maximum amount of land in a parcel upon which buildings, or buildings and other impervious surfaces, can be constructed. Lot coverage caps are defined in the zoning text as a percentage of the lot as a whole.