Census Research Guide: Glossary

Item

Definition

American Community Survey (ACS)

A monthly sample household survey conducted by the Census Bureau to obtain information similar to the long-form census questionnaire. It was first tested in 1995, and replaced the long form for the 2010 Census.The nationwide survey provides annual data for social and economic characteristics for many geographic entities and population groups.

American FactFinder

Replaced by data.census.gov in 2020. An electronic system for access and dissemination of Census Bureau data on the Internet. The system offers prepackaged data products and the ability to build user-selected tables and maps. The system serves as the vehicle for accessing and disseminating decennial/ACS data from 2000- .

apportionment counts

The first data product from the decennial census is the apportionment population for each state and the number of representatives each state is entitled to based on the apportionment calculation.

block

See census block.

block boundary

The features, both visible (street, road, stream, shoreline, and so forth) and invisible (county line, city limit, property line, and so forth), that delimit a census block. A boundary generally must include at least one addressable feature; that is, usually a street or road. The boundary of every legal and statistical entity recognized in the Census Bureau's standard data tabulations is a tabulation block boundary.

block group

A statistical subdivision of a census tract. A BG consists of all tabulation blocks whose numbers begin with the same digit in a census tract; for example, for Census 2000, BG 3 within a census tract includes all blocks numbered between 3000 and 3999. The block group is the lowest-level geographic entity for which the Census Bureau tabulates sample data from the decennial census.

block map

A large-scale map of a single census collection block, showing roads, streets, and other features, together with their names (if any) within and adjacent to the block. Field staff use block maps to guide them in their canvass of each block, to annotate map changes, and, in some areas, to mark (map spot) and number the location of each residential structure.

block number

A number assigned to each census block. For tabulating data for Census 2000, each census block was identified uniquely within a census tract by a 4-digit number. A 1990 census block number had three digits, with a potential alphabetic suffix. The first digit identifies the block group in which the census block is located.

block numbering area

Prior to Census 2000, a statistical subdivision of a county or statistically equivalent entity, delineated by a state government agency or Census Bureau regional census center for the purpose of grouping and numbering census blocks in counties (and statistically equivalent entities) that did not have census tracts. BNAs were discontinued for Census 2000; they were replaced by census tracts in every county and statistically equivalent entity.

census block

An area bounded by visible and/or invisible features shown on Census Bureau maps. A block is the smallest geographic entity for which the Census Bureau collects and tabulates 100-percent decennial census data.

census designated place

A statistical entity that serves as a statistical counterpart of an incorporated place for the purpose of presenting census data for a concentration of population, housing, and commercial structures that is identifiable by name, but is not within an incorporated place. CDPs usually are delineated cooperatively with state, Puerto Rico, Island Area, local, and tribal government officials, based on Census Bureau guidelines. For Census 2000, CDPs did not have to meet a population threshold to qualify for the tabulation of census data.

census geography

A collective term referring to the geographic entities used by the Census Bureau for data collection and tabulation.

census tract

A small, relatively permanent statistical subdivision of a county or statistically equivalent entity, delineated for data presentation purposes by a local group of census data users or the geographic staff of a regional census center in accordance with Census Bureau guidelines. Designed to be relatively homogeneous units with respect to population characteristics, economic status, and living conditions at the time they are established, census tracts generally contain between 1,000 and 8,000 people, with an optimum size of 4,000 people. Census tract boundaries are delineated with the intention of being stable over many decades, so they generally follow relatively permanent visible features. However, they may follow governmental unit boundaries and other invisible features in some instances; the boundary of a state or county (or statistically equivalent entity) is always a census tract boundary.

census tract number

A 4-digit basic number, followed by an optional 2-digit decimal suffix, used to identify a census tract uniquely within a county or statistically equivalent entity. For Census 2000, census tract numbers ranged from 0001 to 9999, with 9400 to 9499 reserved for census tracts related to federally recognized American Indian reservations and off-reservation trust land–primarily reservations and trust land that cross county lines.

Congressional district

One of 435 areas established by law for the election of people to the U.S. House of Representatives. Each district is to be as equal in population to all other districts in the state as practicable, based on the decennial census counts.

Congressional District Data Summary Files

Data files generated for Congressional districts from the decennial census data and made available to the public. They contain the same types of data as the Hundred Percent Summary Files and Sample Data Summary Files.

consolidated metropolitan statistical area

A geographic entity designated by the federal Office of Management and Budget for use by federal statistical agencies. An area becomes a CMSA if it qualifies as a metropolitan area, has a census population of one million or more, has component parts that qualify as primary metropolitan statistical areas based on official standards, and local opinion favors the designation. CMSAs consist of whole counties except for the New England states, where they consist of county subdivisions (primarily cities and towns). See central city and statistical entity.

county

The primary legal division of every state except Alaska and Louisiana. A number of geographic entities are not legally designated as a county, but are recognized by the Census Bureau as equivalent to a county for data presentation purposes. These include the boroughs, city and boroughs, municipality, and census areas in Alaska; parishes in Louisiana; and cities that are independent of any county (independent cities) in Maryland, Missouri, Nevada, and Virginia. They also include the municipios in Puerto Rico, districts and islands in American Samoa, municipalities in the Northern Mariana Islands, and islands in the Virgin Islands of the United States. Because they contain no primary legal divisions, the Census Bureau treats the District of Columbia and Guam each as equivalent to a county (as well as equivalent to a state) for data presentation purposes. In American Samoa, a county is a minor civil division.

decennial census

The census of population and housing, taken by the Census Bureau in each year ending in zero. Article 1, Section 2 of the Constitution requires that a census be taken every 10 years for the purpose of apportioning the U.S. House of Representatives. The first census of population was taken in 1790. The Census Bureau first conducted the census of housing in 1940.

economic census

The collective name for the censuses of construction, manufactures, minerals, minority- and women-owned businesses, retail trade, service industries, transportation, and wholesale trade, conducted by the Census Bureau every five years in years ending in 2 and 7.

Federal Information Processing Standards (FIPS)

A set of numeric and/or alphabetic codes issued by the National Institute of Standards and Technology to ensure uniform identification of geographic entities (and other electronic data) throughout all federal government agencies. The entities covered are states, counties, metropolitan areas, Congressional districts, named populated and other locational entities (such as places, county subdivisions, and American Indian and Alaska Native areas), and geopolitical entities of the world.

geocode (geographic code)

A code used to identify a specific geographic entity. For example, the geocodes needed to identify a census block for Census 2000 data are the state code, county code, census tract number, and block number. Every geographic entity recognized by the Census Bureau is assigned one or more geographic codes.

Geographic Comparison Table

A table in the American FactFinder that provides census data for one or more selected sets of geographic entities of the same type; e.g., data for all counties in a state.

housing unit

A single-family house, townhouse, mobile home or trailer, apartment, group of rooms, or single room that is occupied as a separate living quarters or, if vacant, is intended for occupancy as a separate living quarters.

hundred percent data

Population and housing information collected for all living quarters in the United States. These questions appeared on both the short- and long-form questionnaires. The questions include age, Hispanic or Latino origin, race, relationship to the householder, sex, and whether the housing unit is owned or rented.

long form

The decennial census questionnaire containing 100-percent and sample questions. Replaced by the ACS.

mean

The arithmetic average of a set of numbers.

median

The middle value in a set of numbers.

metropolitan area

A large population nucleus, together with adjacent communities that have a high degree of economic and social integration with that nucleus. This collective term was established by the federal Office of Management and Budget (OMB) in 1990 to refer to metropolitan statistical areas, consolidated metropolitan areas, primary metropolitan statistical areas, and New England County Metropolitan Areas.

metropolitan statistical area

A geographic entity designated by the federal Office of Management and Budget for use by federal statistical agencies. An MSA consists of one or more counties, except in New England, where MSAs are defined in terms of county subdivisions (primarily cities and towns).

migration

A change of a household's or person's residence from 5 years ago.

P.L.

See "Public Law 94-171"

population

All people living in a geographic area.

Population and Housing Characteristics

A series of Census 2000 reports containing tables that report population and housing data. The series is available in printed form and on the Internet in PDF format. It is comparable to the 1990 census's CPH (Census of Population and Housing) series of reports.

population density

The population of an area divided by the number of square miles or square kilometers of land area.

Public Law 94-171

A 1975 law that requires the Census Bureau to provide state governments with selected decennial census data tabulations and related geographic products for specific geographic entities by April 1 of the year following the census. These data and products are used by the states to redefine their Congressional districts and the areas used for state and local elections–a process called redistricting.

Public Law 94-171 Summary Files

Data provided in response to the requirements of P.L. 94-171, by census tract and census block, including four matrixes: data for race, Hispanic or Latino and not Hispanic or Latino, race for the population 18 years and older, and Hispanic or Latino and not Hispanic or Latino for the population 18 years and older.

public use microdata area

A geographic entity for which the Census Bureau provides specially selected extracts of raw information from a small sample of long-form census records. PUMAs, which must have a minimum census population of 100,000 and cannot cross a state line, receive a 5-percent sample of the long-form records; these records are presented in state files. These PUMAs are aggregated into "super-PUMAs," which must have a minimum census population of 400,000 and receive a 1-percent sample in a national file. PUMAs for Census 2000 were delineated by state officials, and comparable officials in the District of Columbia and Puerto Rico. The Census Bureau provided a single 10-percent sample file each for Guam and the Virgin Islands of the United States.

public use microdata sample

Computerized files containing a small sample of individual long-form census records showing the population and housing characteristics for the unidentified people included on those forms. The records are screened to maintain confidentiality.

reapportionment

The redistribution of seats in the U.S. House of Representatives among the several states on the basis of the most recent decennial census, as required by Article 1, Section 2 of the Constitution.

redistricting

The process of revising the geographic boundaries of areas from which people elect representatives to the U.S. Congress, a state legislature, a county or city council, a school board, and the like to meet the legal requirement that such areas be as equal in population as possible following a census.

sample data

Census data derived from additional questions asked of about 17 percent of the population on the long-form questionnaire for Census 2000, and on a continuous basis for areas covered by the American Community Survey. The person questions cover social characteristics, such as ancestry, disability, grandparents as caregivers, education, marital status, and veteran status, and economic characteristics, such as 1999 income and work status and industry, occupation, and class of worker. The housing questions cover physical characteristics, such as the number of rooms, type of heating fuel, and telephone service availability, and financial characteristics, such as rent, mortgage, utilities, taxes, and fuel costs.

Sample Data Summary Files

Files generated from the decennial census data and made available to the public. They include social, housing, and economic characteristics. Summary File 3 presents population counts for ancestry groups. Summary File 4 presents population and housing unit characteristics iterated for many detailed race and Hispanic or Latino categories, American Indian and Alaska Native tribes, and ancestry groups.

sampling error

An error that occurs because only part of the population is contacted directly. As with any sample, differences are likely to exist between the characteristics of the sampled population and the larger group from which the sample was chosen. Sampling error, unlike nonsampling error, is measurable.

short form

The decennial census questionnaire containing only the 100-percent questions.

special census

A federal census conducted at the request and expense of a local governmental agency to obtain a population count between decennial censuses.

Summary File

One of series of Census 2000 state and national computer files containing great subject matter detail for a large number of geographic entities, ranging down to the block group or census block.

Summary File 1

This Census 2000 file presents 100-percent population and housing data for the total population, for 63 race categories, and for many other race and Hispanic or Latino categories. The data include age, sex, households, household relationship, housing units, and tenure (whether the residence is owned or rented). Also included are selected characteristics for a limited number of race and Hispanic or Latino categories. The data are available for the U.S., census regions, census divisions, states and statistically equivalent entities, counties and statistically equivalent entities, county subdivisions, places, census tracts, block groups, census blocks, metropolitan areas, urban areas, American Indian and Alaska Native areas, tribal subdivisions, Hawaiian home lands, Congressional districts, and ZIP Code tabulation areas. Data are available down to the block level for many tabulations, but only to the census tract level for others.

Summary File 2

This Census 2000 file presents data similar to the information included in Summary File 1. These data are shown down to the census tract level for 250 race, Hispanic or Latino, and American Indian and Alaska Native categories. For data to be shown in SF 2, a population category must meet a population size threshold of 100 or more people of that specific population category in a specific geographic entity.

Summary File 3

This Census 2000 file presents data on population and housing long-form subjects, such as income and education. It includes population totals for ancestry groups. It also includes selected characteristics for a limited number of race and Hispanic or Latino categories. The data are available for the U.S., census regions, census divisions, states and statistically equivalent entities, counties and statistically equivalent entities, county subdivisions, places, census tracts, block groups, metropolitan areas, urban areas, American Indian and Alaska Native areas, tribal subdivisions, Hawaiian home lands, Congressional districts, and ZIP Code tabulation areas.

Summary File 4

This Census 2000 file presents data similar to the information included in Summary File 3. The data are shown down to the census tract level for 336 race, Hispanic or Latino, American Indian and Alaska Native, and ancestry categories. For data to be shown in SF 4, there must be at least 50 unweighted sample cases of a specific population category in a specific geographic entity. In addition, data for the specific population category for the specific geographic entity must have been available in Summary File 2.

Summary Tape File

One of series of four 1990 census summary tabulations of hundred percent data and sample population and housing data, available for public use on computer tape, CD-ROM, and the Internet. These files were not produced after Census 1990.

township

A type of minor civil division in 16 states. In some states, many or all townships are nonfunctioning entities. In Michigan, some townships are legally designated as "charter townships."

tract

See census tract.

tract number

See census tract number.