Introduction to U.S. Census/ACS Data at CSSCS - Required by the U.S. Constitution

Sep 21, 2026

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Required by the U.S. Constitution, the U.S. decennial Census counts population and housing every ten years, while the American Community Survey (ACS) supplies ongoing local community characteristics through single-year, 3-year, and 5-year estimates. CSSCS serves as a distribution center providing Census and ACS files from 1980–2010 and 2005–present, including STF/SF and PUMS/ACS-PUMS in multiple software formats, plus retrieval help via IPUMS-USA. The text explains how seats in Congress are apportioned using Census/ACS data and how these data support redistricting, funding allocation, public policy, and planning. It details STF/SF summary products and PUMS microdata use, geography levels, and TIGER/Line geographic encoding for mapping with GIS tools.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages5

Reading Time13 min

AccessFree to download

U.S. Census and ACS Overview

Decennial Census requirement and ACS purpose

Census/ACS Data Products at CSSCR

Data coverage and retrieval support

STF/SF summary files

PUMS microdata files and geography levels

TIGER/Line geographic products

Introduction to U.S. Census/ACS Data at CSSCS Updated by Tina Tian Center for Social Science Computation & Research 110 Savery Hall University of Washington Seattle WA 98195 U.S.A. (206)543-8110 August 2010 [http://julius.csscr.washington.edu/pdf/census10](http://julius.csscr.washington.edu/pdf/census10) Required by the U.S. Constitution, the U.S. decennial Census has been conducted every ten years since 1790 to count the population and housing units for the entire nation. The American Community Survey (ACS) is a new approach to producing critical information about the characteristics of local communities. It will eliminate the need for a long form in the 2010 Census and is a key part of the Census Bureau’s Decennial Census Program. Started in 2006, every year the ACS can support the release of single-year estimates for geographic areas with populations of 65,000 or more; also accumulate sample over 3-year produce estimates for geographic areas with populations of 20,000 or more, and 5-year intervals to produce estimates for smaller geographic areas including census tracts and block groups. The Census/ACS provides population counts that determine how seats in the U.S. House of Representatives are apportioned. Census/ACS data are also widely used in drawing congressional and state legislative boundaries, allocating federal and state funds, formulating public policy, and assisting with planning and decision-making in the public and private sectors. Census/ACS Files Available at CSSCR As one of the distribution centers for the Census Bureau’s electronic products, CSSCR houses Census data from 1980-2010 and ACS 2005-Present, including Summary Tape Files (STF), Summary Files (SF/ACS-SF) and Public Use Micro Samples (PUMS/ACS-PUMS) in varies of statistical software formats . On request, we also help retrieve historical U.S. Census data from the IPUMS-USA database available at [http://www.ipums.org](http://www.ipums.org. IPUMS-USA is a comprehensive)[. IPUMS-USA is a comprehensive](http://www.ipums.org. IPUMS-USA is a comprehensive)[ ](http://www.ipums.org. IPUMS-USA is a comprehensive)national census database containing integrated microdata from 1850 to the current. We host a website for the Washington State decennial Census data files and documentation at [http://julius.csscr.washington.edu/Decennial%20Census.htm](http://julius.csscr.washington.edu/Decennial%20Census.htm), and ACS data files and documentation. [http://julius.csscr.washington.edu/american_community_survey.htm](http://julius.csscr.washington.edu/american_community_survey.htm. In addition)[. In addition](http://julius.csscr.washington.edu/american_community_survey.htm. In addition), CSSCR also distributes some TIGER/Line files, a Census geographic product. STF/SF and PUMS are two major types of Census/ACS data products. STF/SF contains tabulated summary statistics for different levels of Census geography from the nation, the state, the county, down to the city block. STF/SF 1 and 2 present tabulated data from the Census short-form (100%) questionnaire. STF/SF 3 and 4 present cross-tabulations of information from the long-form (sample) questionnaire. Tables in STF/SF 2 and 4 are iterated for many detailed racial groups, as well as American Indian and Alaska Native tribes. In SF 4, many data are also tabulated by detailed ancestry groups. PUMS files present a sample of individual records of responses to the long-form questionnaire with unique identifiers (such as addresses, names, etc.) removed to protect individual confidentiality. Different from the STF/SF which provides summary data information for a specific geographic entity, in PUMS, the basic unit of analysis is a housing unit or a person. PUMS files allow users to prepare their own customized tabulations of most population and housing subjects. There are two sets of PUMS: 5-percent sample file (PUMS-A file) and 1-percent sample file (PUMS-B file). Besides the obvious difference in sam

FAQs

What is the relationship between the U.S. decennial Census and the American Community Survey (ACS)?

The decennial Census counts population and housing units every ten years, while the ACS provides critical information about local community characteristics. The ACS reduces the need for a long-form in the 2010 Census and supports ongoing estimation for areas of different population sizes.

What kinds of Census/ACS files does CSSCR provide?

CSSCR houses Census data from 1980–2010 and ACS data from 2005–present, including Summary Tape Files (STF), Summary Files (SF/ACS-SF), and Public Use Micro Samples (PUMS/ACS-PUMS) in various statistical software formats. It also supports retrieval of historical Census data from IPUMS-USA and distributes some TIGER/Line files.

How do STF/SF and PUMS differ for analysis?

STF/SF provides tabulated summary statistics for geographic entities, such as nation, state, county, and down to city blocks. PUMS provides microdata records for individuals or housing units (with identifiers removed), enabling users to create customized tabulations.

Sep 21, 2026

Uploaded by Đào