An Introduction to Census Resources

Data and Program Library Service

An Introduction to Census Resources

This primer is divided into sections that discuss various aspects of the Census such as geography, outlines of printed and machine readable products, sampling and the presentation of data, and links for finding further information. Users should note that many of these resources are now available on the Internet. We encourage you to make use of the DPLS Internet Crossroads section for further information, and also look at our Data Alerts and Info page for important updates on Census data.

Introduction
Understanding Census Geography
Census Print and Data Products
Census Bureau Information Services
Value-added Vendors

Introduction

The U.S. Constitution requires the government to conduct a census of the population every 10 years for the purpose of apportioning the representation of the citizens according to their numbers. The immediate reason for conducting the census is to count all the people within their geographical locations. The primary challenge is to locate everyone in their homes, count them, determine male and female populations, the ages of the members of the households. Prior to the middle of the 20th century, the census was simple and straight forward, reflecting the limited role the government played in everyday life.
Over time, the government has played a more active role in the lives of its citizens; each increase in government activity has led to an increase in the amount of information it has needed to formulate policy. To gather more information, it has been necessary to draw a sample of the population, as it would be too expensive to poll every single person. With the use of sampling techniques, analysts have been able to study in great detail a smaller portion of the population from which they can infer characteristics of the population in general. At the same time, the need for an exact count of the population has remained. The result has been that there are two sets of Census data--a broad look at the whole population on a narrow range of questions and a closer look at a sample of the population on a deep range of questions. As the government collects more information from people, two complicating issues have arisen: the need to protect the confidentiality of respondents and the infeasibility of every single individual providing the depth of information needed to set policy.

For purposes of counting the population, the Census Bureau polls 100% of the households in the United States with a brief questionnaire asking a limited number of questions about every household member and a number of questions about the household itself. For learning about the lives of the people, the Census Bureau sends a longer questionnaire to two samples of the households (a 5% sample and a second 1% sample of all households), which asks very detailed questions about the members of the household and of the household itself.

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Understanding Census Geography

Territorial Organization and Census Geography

Since the original purpose of the census was to guarantee proportionate representation to the citizens of the United States, the census must initially count all of the residents of every state. The territory of the United States is organized hierarchically for the purpose of subdividing the population in order to obtain the most accurate count of all people in their place of residence. The basic organization is like this:
- National (United States)
  - States (50 states plus the District of Columbia)
    - Counties
      - County sub-divisions
        
        Census Tracts/Block Numbering Areas
        
        Block Groups
        
        Blocks
This scheme does not show all of the various ways in which census geography is presented in its publications and other data products. The United States can be divided in three manners: regions, divisions, or the states. The sum of the populations of each of these three groupings is equal to the sum for the entire United States. Similarly, besides county subdivisions, states can also be divided into Congressional Districts (the original purpose of the Census) and into ZIP Code areas. Congressional Districts, like counties, cover 100% of a state's territory and account for 100% of a state's population. Zip Code areas, on the other hand, do not account for 100% of a state's territory. (Whereas unoccupied areas have census and congressional competence, mail is not delivered where there are no addresses or where no one lives.)

Within each state there are also concentrations of people in some areas, while others are sparsely populated. States are divided to assure a level of administrative burden sharing within for the provision of education, infrastructure, and other community services. Frequently, the concentrations of the populace and the administrative divisions have not exactly coincided. The Census Bureau has divised a number of mechanisms to assure everyone is counted, but the population can be measured according to a variety of geographic criteria.
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General Outline of 1990 Census Geography

 Summary   No. of
 Level     Units   Geographic Description

  010          1    United States
  020          4    Regions
  030          9    Divisions
  040         51    States, plus District of Columbia
  050      3,141    Counties
  060     35,298    County sub-divisions
  070     23,788    Places/remainders
  080     61,231    Census Tracts/Block Numbering Areas
                            (43,691 Tracts/3,423 BNAs)
  090    226,399    Block Groups
  100  6,961,148    Blocks

State Subdivision Variations

 3,141      Counties
   435      Congressional Districts
29,469      Zip Code Areas (There are about 8,000 zip code areas that
                  are only commercial.)

Covering less than 100% of the population and geography

           Places (crossing county divisions)
           Indian reservations, trusts, etc.
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Census Print and Data Products

The 100% population data are released in two formats, printed books and machine readable form. The 100% count publications include the CP-1 (General Population Characteristics) and the CH-1 (General Housing Characteristics). There are two sets of machine readable formats: the PL 94-171 data summarizing all questions down to the tract level--for the purposes of reapportionment--and the Summary Tape Files 1 and 2, which provide comparative summaries for the 100% population counts.
The sample data are also released in printed and machine readable form. Sample publications include CP-2 (Social and Economic Characterisitcs) and CH-2 (Detailed Housing Characteristics). There are two sets of machine readable formats: the Summary Tape Files 3 and 4, which provide statistics for the samples of the population, and the Public Use Microdata Series (PUMS) which consist of the actual sample data with most geographical identifiers removed. The 1990 Census has released three PUMS versions--the full 5% (1 in 20) sample (consuming about 25 reels of computer tape or 7 CD/ROM disks), a (1 in 100) 1% sample (about 5 reels of computer tape or 2 CD/ROM disks), and a .1% (1 in 1,000) sample (one tape).

Major Print Series From the 1990 Census

The 1990 Census of Population and Housing reports are available at the Government Documents Library at the State Historical Society.
Population

CP-1 GeneralPopulation Characteristics
- This report series provides detailed statistics on age, sex, race, Hispanic origin, and marital status derived from the 100% data. Data are available for census geography at the state, county, place and MCD levels for areas with 1,000 or more inhabitants.
CP-2 Social and Economic Characteristics
- These reports provide data focusing on population subjects such as income, education, and occupation. These sample data are available for states, counties, places, MCDs, and American Indian and Alaska Native areas.
Housing

CH-1 General Housing Characteristics
- These reports provide detailed statistics derived from the 100% data on housing questions, including units in the structure, tenure, and value and rent. Data are presented for the census geography on the same level as the CP-1 Series.
CH-2 Detailed Housing Characterisitics
- This report series summarizes the sample data relating to housing questions such as the number of bedrooms, plumbing and kitchen facilities, telephone, and source of water. Data are published for states, counties and places, and MCDs with 2,500 or more inhabitants.
Population and Housing

CPH-1 Summary Population and Housing Characteristics
- This report series provides total population and housing units counts as well as summaries of the statistics contained in the CP-1 and CH-1 series. Reports cover states, local governments, and American Indian and Alaska Native areas. A U.S. Summary is issued as well as reports for each state.
CPH-2 Population and Housing Unit Counts
- This series contains data on total population and housing unit counts for 1990 and previous decennial censuses, listed for states, counties, MCDs, places, state component parts of MAs and UAs, and summary geographic areas.
Population and Housing Characteristics for Census Tracts and Block Numbering Areas
- Data on most 1990 census subjects are shown for census tracts in MAs and census tracts or BNAs in the remaining (non-MA) portions of each state. Some tables use 100% data while other use sample data.
Population and Housing Characteristics for Congressional Districts of the 103rd Congress, (C3.223/20:990 CPH-4-#)
- These reports show population and housing data for congressional districts as well as counties, places, and MCDs.
Summary Social, Economic, and Housing Characteristics (C3.223/23:990 CPH-5-#)
- This report series is a companion volume to CPH-1 and provides data on sample subjects for local governments, including American Indian and Alaska Native areas.
Summary Social, Economic, and Housing Characteristics--outlying areas (C3.223/23:990 CPH-6-#)
- This report series contains data on the same subjects as the CPH-5 series, but this series covers data for the outlying areas of the United States (i.e., territories and possessions that such as Puerto Rico, Guam, and the Virgin Islands).
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Census Data Products

The Census Bureau has released a large portion of the 1990 Census on CD-ROM as well as on computer tape. Most of these CD-ROMs are available on this campus, many at the DPLS. The CD-ROMs were created from the original computer tapes and have made access to census data easier than ever before. Data can be browsed using Go, a menu-driven software developed by the Census Bureau, or special subsets of data can be created using Extract, a more complex software.

Summary Tape Files

STF 1 Summary Tape File 1--100% data of population and housing
- STF 1A: all geographic areas down to the block-group level.
- STF 1B: all geographic areas down to the block level.
- STF 1C: United States, regions, divisions, states, counties, MAs.
  Technical documentation is available..
STF 2 Summary Tape File 2--100% data with more subject detail.
- No CD-ROMs will be released with these data; Tape data are available through the DPLS
STF 3 Summary Tape File 3--sample data of population and housing.
- STF 3A: all geographic areas down to the block-group level.
- STF 3B: data summarized for 5-digit ZIP codes.
- STF 3C: data for United States, regions, divisions, and states.
  Technical documenation is available.
STF 4 Summary Tape File 4--sample data with more subject detail.
- No CD-ROMs will be released with these data; Tape data are available at the DPLS
Other Data Products

PL 94-171 Public Law 94-171 Redistricting Data File
- This data file presents the preliminary census counts designed and formatted for use in legislative redistricting. Data for areas down to the block level, tracts/BNAs and voting districts include population, racial composition, Hispanic origin, age, and housing units.
EEO Census/Equal Employment Opportunity Special File
- This file provides 1990 census sample data with particular relevance to EEO and Affirmative Action uses. Data tabulations include detailed occupation by age and educational attainment by age and are included down to the county level.
PUMS Public Use Microdata Samples
- These files contain raw, sample data from which the STF 3 and STF 4 files were created, but in which geographic identifiers exist only for population groups of 100,000 or more. EDS has CD-ROM and computer tape files of the 5% and 1% data for all 50 states, plus the District of Columbia.
  Technical documentation is available.
TIGER TIGER/Line 1992
- These CDs contain digital mapping software that use census produced data files to create County level maps displaying major geographical features, and which can interact with other Census CD products. The map coordinates can also be used with other mapping products to create customized maps.

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The Bureau of the Census Information Services

The Bureau is responsible for conducting and disseminating the results of the U.S. decennial census as well as other major surveys. It supports a very robust Web Site which provides contact information, access to data and interactive software. Users' Services is responsible for a broad program of assistance to census data users including distributing selected census products, providing training, producing statistical compendia, and handling user inquiries. The annual Census Bureau Catalog and Guide lists products released. The ICPSR has signed a joint statistical agreement with the Bureau of the Census to distribute 1990 Census data through the ICPSR.

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Value-added Vendors

There are numerous products produced by third-party vendors which repackage Census data, providing enhanced access often at significant expense. The DPLS has several of these products, which can be identified via our on-line catalog and used in the library.

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