Block Group
A Block Group is a cluster of Census Blocks within a given Census Tract and usually covers a contiguous area. Each Census Tract contains at least one Block Group. Block groups are uniquely numbered within each Census Tract.
Block Groups never cross county or Census Tract boundaries, but may cross the boundaries of native areas/Hawaiian home lands or of county subdivisions (places, urbanized areas, voting districts, or Congressional districts). Within native area/Hawaiian home land census geography, Census Tracts and Block Groups are defined with native entities, and can cross county and state boundaries. These are commonly referred to as tribal Block Groups.
Block Groups generally have a population of between 600 and 3,000, with an optimum size being 1,500 inhabitants. Most Block Groups were delineated by participants in the Census Bureau’s Participant Statistical Areas Program. The Census Bureau only delineated Block Groups where a local or tribal government declined to participate in the program, or where a potential local participant could not be identified.
Census Block
A Census Block is the smallest geographic unit for which the Census Bureau tabulates data. Census Blocks are generally bounded by streets, legal boundaries, or other features. Approximately 8.5 million Census Blocks were identified in the 2020 US Census.
Census Tract
Census Tracts are small, relatively permanent statistical subdivisions of counties, delineated for the purpose of presenting decennial census data.
Census Tract boundaries are always nested within county boundaries. Census Tract boundaries normally follow visible features, but may governmental unit boundaries or other non-visible boundaries in some instances.
Census Tracts are delineated by the Census Bureau every ten years in preparation for each census. Local census area committees review these definitions in cooperation with the Census Bureau. The Census Bureau delineates Census Tracts without local participation only when no local participant can be identified, or when local or tribal governments decline to participate in the review process.
Census Tracts generally have a population between 1,500 and 8,000 residents with relatively homogenous population characteristics, economic status, and living conditions.
Census Tracts are identified by a four-digit basic number ranging from 0000 to 9999. The basic number is unique within each county (or equivalent area). Tract numbers may contain an optional two-digit suffix ranging from .01 to .98. The Census Bureau assigns a default tract number of 0000 to some coastal and territorial sea waters in lieu of extending the Census Tract boundary into the water feature.
Core Based Statistical Area (CBSA)
A Core Based Statistical Area (CBSA) consists of a county containing an incorporated place or Census Designated Place (CDP), and has a population of at least 10,000. A CBSA may include adjacent counties if at least 25 percent of the residents of those counties work in the CBSA’s core county.
CBSAs are categorized as either metropolitan or micropolitan. These CBSA classifications cover approximately 90 percent of the US population, allowing for data collection and aggregation for less-urban areas. Metropolitan statistical areas have at least one urbanized area with a population of at least 50,000 residents. Micropolitan statistical areas must have at least one urban cluster and a population of at least 10,000, but less than 50,000. If specific criteria are met, a metropolitan statistical area with a population of 2.5 million or more may be subdivided to form smaller groupings known as metropolitan divisions.
Under CBSA standards, a county in which at least half the population resides in urban areas, each with a population of 10,000 or more, or that has at least 5,000 people residing in a single urban area with a population of 10,000 or more is identified as a central county. Outlying counties may be included in the CBSA if at least 25 percent of the employed residents of the outlying county commute to/from the CBSA’s central county.
As part of maintenance by the Census Bureau, CBSAs are updated based on the Office of Management and Budget’s (OMB’s) most recent definitions. The AP (Census Place) layer is updated to TIGER 2020 definitions and population figures were also updated. Census Blocks, Census Block Groups, and Census Tracts are renumbered based on 2020 Census boundary definitions.
Combined Statistical Area (CSA)
The OMB defines Combined Statistical Areas (CSAs) as combinations of adjacent Metropolitan Statistical Areas (MSAs) and Micropolitan Statistical Areas (µSAs) in the 50 states and Puerto Rico, that can demonstrate economic or social linkage. CSAs consist of various combinations of adjacent metropolitan and micropolitan areas with economic ties measured by commuting patterns. The areas that combine to form a CSA retain their own designations as metropolitan or micropolitan statistical areas within the larger CSA.
The primary factor distinguishing a Combined Statistical Area from a Metropolitan Statistical Area or a Micropolitan Statistical Area is that the social and economic ties between the individual MSAs/ µSAs within a CSA are lower than between the counties within an MSA.
CSAs represent multiple metropolitan or micropolitan areas that have an employment interchange of at least 15%. They also often represent regions with overlapping labor and media markets.
Refer to online OMB Bulletins for additional information about Combined Statistical Areas.
County
Counties are the primary legal divisions of states. In the state of Louisiana, these divisions are known as parishes. Alaska has no counties; statistically equivalent entities are termed boroughs, cities and boroughs, or municipalities. Alaska also contains entities called census areas, which are cooperatively delineated by the state of Alaska and the Census Bureau for statistical purposes.
Four states – Maryland, Missouri, Nevada, and Virginia – have one or more incorporated places that are independent of any county and thus constitute the primary divisions of their respective states. These incorporated places are known as independent cities and are treated as statistically equivalent entities. The District of Columbia has no primary divisions; the entire district is treated as a statistically equivalent entity. In Puerto Rico, municipios are the statistically equivalent entities of counties.
Minor Civil Division (MCD)
Minor Civil Divisions (MCDs) represent different legal entities with a variety of governmental and/or administrative functions:
- Native reservations
- Assessment districts
- Boroughs
- Election districts
- Grants
- Locations
- Magisterial districts
- Parish governing authority districts
- Plantations
- Precincts
- Purchases
- Road districts
- Supervisors’ districts
- Towns
- Townships
The Census Bureau recognizes MCDs in 28 states and Puerto Rico. Since the District of Columbia has no primary divisions, it is considered the equivalent to an MCD for statistical purposes.
MCDs in the following states also serve as general-purpose local governments and can perform the same governmental functions as incorporated places:
- Connecticut
- Maine
- Massachusetts
- Michigan
- Minnesota
- New Hampshire
- New Jersey
- New York
- Pennsylvania
- Rhode Island
- Vermont
- Wisconsin
In some states, all or some of the incorporated places are not part of an MCD. These places have a unique MCD FIPS code that is the same as the Place FIPS code. In addition to being independent of an MCD, incorporated places can also be located in more than one MCD.
Place
A Place is a concentration of population, either legally bounded as an incorporated place, or identified by the Census Bureau as a Census Designated Place (CDP). Places can be categorized as legal entities, statistical entities, or corporate corridors and offset corporate boundaries.
Legal Entities
Legal Entities can be either consolidated cities or incorporated places.
Consolidated Cities
A consolidated government is one in which the functions of an incorporated place and its county or MCD are merged. The primary incorporated place and county/MCD continue to exist as legal entities, even though it performs few, if any, governmental functions and has no elected officials. In these cases, and when one or more other incorporated places in the county/MCD continue to function as separate governments (even though they are included in the consolidated government), the primary incorporated place is referred to as a Consolidated City. Consolidated Cities must include at least 90 percent of the population of their parent county. In some instances, the entire population of the parent county resides in the consolidated city.
The Census Bureau classifies incorporated places within a Consolidated City as Place entities and creates a separate Place (balance) record for the portion of the consolidated city that is not a part of any other Place
Incorporated Places
Incorporated Places are those Places reported to the Census Bureau as being legally in existence under the laws of their respective states as of the latest Boundary and Annexation Survey (BAS). As opposed to MCDs, which are usually created to provide services or administer an area without regard to population, incorporated places are established to provide governmental functions for a concentration of people.
Incorporated Places vary in population and geographic area, and may span county or county subdivision boundaries.
For census purposes, incorporated places exclude:
- Boroughs in Alaska (treated as statistical equivalents of counties)
- Towns in the New England states, New York, and Wisconsin (treated as MCDs)
- Boroughs in New York City (treated as MCDs)
- Balance portions of consolidated cities (treated as Incorporated Places)
- Independent cities in Maryland, Missouri, Nevada, and Virginia
Statistical entities
Statistical entities can be either Census Designated Places (CDPs) or Consolidated City remainder portions.
Census Designated Places (CDPs)
A Census Designated Place is a settled concentration of population that is identifiable by name but is not legally incorporated under the laws of the state in which it is located. For census purposes, CDPs are treated as the statistical counterparts of incorporated places.
CDP boundaries are usually defined in cooperation with local or tribal officials. These boundaries generally coincide with visible features or the boundaries of adjacent incorporated places (or the boundaries of other legal entities) and have no legal status, nor do they have municipal governments consisting of elected officials. Boundaries of Census Designated Places change with settlement patterns and may not be identical from one decennial census to the next. There are no population size requirements for CDPs.
Hawaii and Puerto Rico do not have incorporated places. All places in Hawaii and Puerto Rico are CDPs. CDPs in Puerto Rico are called comunidades or zonas urbanas.
Consolidated City remainder portions
Consolidated City remainder portions are those areas of a consolidated city that are not included in another incorporated place.
Offset corridors and corporate limit offset boundaries
A corporate corridor is a narrow, linear part of an incorporated place (or, in rare instances, another legal entity) that includes the street/right-of-way, or the portion of a street/right-of-way, within the incorporated place. It excludes from the incorporated place any structures (houses, apartments, or businesses) with frontage along the street.
A corporate limit offset boundary is an incorporated place boundary that lies along only one side of a street. It may include all or part of that street but does not include any structures or land adjoining the side of the street with the corporate limit offset boundary.
Multiple corporate limit offset boundaries may exist in the same street/right-of-way. Corporate limit offset boundaries use the same map symbology as non-offset boundaries.