Census and Redistricting Data FAQs

8/9/2021

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Below are a list of frequently asked questions and their answers related to the census and redistricting.

When is the 2020 census released?

Since the 1980 cycle, the U.S. Census Bureau has provided two legally required data releases after the census is completed, one that focuses on congressional apportionment—state total population—and one that provides details about the nation down to a granular level for use in redistricting.

When was the census data released this cycle that determines how many seats in Congress each state will have for the next decade?

April 26, 2021. The 2020 apportionment population counts were delivered to President Joe Biden and the president sent apportionment numbers to Congress on April 26, 2021.

What do the apportionment results tell us?

This first data release includes the total population in the nation and in each state and shows the percentage change since the 2010 census. The nation as grew 7.4%, the lowest growth rate since the 1930s.

When will the detailed data for redistricting be delivered?

The Census Bureau plans to release the same detailed data (also known as redistricting data, Public Law 94-171 data, or P.L. data) in two formats. By Aug. 12, it will release the data in what it calls a “legacy format,” which means it will be made available to states and the public, through the Bureau’s website, as zip files. Data specialists will need to import these files into a database and build relationships between the various files to query and extract data from them. The same redistricting data will be released by Sept. 30 through the Census Bureau’s data.census.gov online web tool. The September release will be in format that will make it easier to view and download the tables from the P.L. 94-171 data.

Will the data from the August release be the same as the data from Sept. 30?

Yes. The data will be exactly the same.

What is considered by the U.S. Census Bureau to be the 'official' release of the redistricting data?

The data included in the August and September deliveries will be identical. States can use either the August delivery or the September delivery as appropriate, taking their own statutes and constitutional requirements into account.  The Census Bureau considers both releases to be official and fit for use. 

Who receives the redistricting data?

Governors, state majority and minority legislative leaders, redistricting commissions, as well as state redistricting data program liaisons will all be mailed a DVD and flash drive with their state’s data. The Secretary of Commerce is required, under 13 U.S. Code § 141(c), to furnish the governor and other state officials having responsibility for legislative apportionment or districting with population counts for American Indian areas, counties, cities, census blocks and state-specified congressional, legislative and voting districts.

How will the state totals reported for apportionment be different than the state totals reported in the redistricting data?

Apportionment data includes military and civilian employees who are stationed overseas and are only attributed at the whole state level. These individuals are not included in the redistricting data which includes lower levels of geography, such as counties, cities and census blocks. Service members who are merely deployed abroad (and thus keep a stateside address) are counted at that address and therefore are included for redistricting and other census data. This distinction means state total populations will be slightly lower in the redistricting data file than in the apportionment data.  However, the state resident population reported as one part of the apportionment counts will be equal to the state resident population in the redistricting data.

How does PL data compare to data from the American Community Survey?

The bureau has released a fact sheet, Which Data Set is Right For Me?, on its data sources. It provides a comparison between decennial census data — what we all think of as “the census”— and its annual population estimates and the American Community Survey (ACS) one-year and five-year estimates.

How does the bureau keep respondent’s data private?

Federal law (13 U.S. Code §§ 9 and 214) requires the protection of collected data and ensures the confidentiality of all respondents. It is illegal for any bureau employee to disclose or publish any census or survey information that identifies an individual or business. In 2010, the bureau used swapping  as its disclosure avoidance technique. This cycle the bureau plans to use differential privacy, a method that “injects noise” into the redistricting data. There will be no noise injected at the state total population level, but there will be noise injected into all other levels of geography, including congressional districts down to townships and census blocks.

Why is the bureau using differential privacy method for the 2020 redistricting data?

The bureau needed a new disclosure avoidance technique to contend with technological advances, such as greater computing power, advances in mathematics and the growth of other databases such as those used by commercial data vendors.

How will differential privacy affect apportionment and redistricting data?

Apportionment data is not affected by differential privacy. State total populations are reported to the public as they were enumerated. For all other purposes, differential privacy will be applied and thus the data will be “noisy” to some extent, mostly at small geographic levels.

Will differential privacy be significant for redistricting?

Some say yes, others say no. See our webpage, Differential Privacy Explained. With what we know now, differential privacy-based distortions will be more significant for small units of geography and small minority and ethnic groups.

Are there other data releases from the U. S. Census Bureau?

Yes. The bureau conducts more than 130 surveys and programs each year. The bureau releases the American Community Survey estimates, total and voting-age population estimates, demographic analysis estimates and many other data products throughout the decade. These are used for many kinds of policymaking and financial decisions in the public and private sectors.

Who can I contact for more information?

NCSL: Wendy Underhill (wendy.underhill@ncsl.org) and Christi Zamarripa (christi.zamarripa@ncsl.org). Census: U.S. Census Bureau’s Redistricting & Voting Rights Data Office, (RDO@census.gov).

Additional Resources