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Explainer

The Census Redistricting Data Release, Explained

States will use the information to draw voting maps that will be in use for 10 years.

Last Updated: August 12, 2021
Published: August 10, 2021

On August 12, the Census Bureau released the most detailed results from the 2020 Census so far. The numbers in this redis­trict­ing data file will enable states and local­it­ies to begin the once-a-decade redraw­ing of elect­oral districts. The bureau has said that it will also release the same inform­a­tion in a more user-friendly format by Septem­ber 30.

The redis­trict­ing process is very import­ant because it can influ­ence who gets elec­ted, how vari­ous communit­ies are repres­en­ted, and the ways public resources are distrib­uted.

What did the Census Bureau release on August 12 and how will it be used?

The bureau released the detailed data that states and local govern­ments need to redraw elect­oral district bound­ar­ies. In contrast to earlier census releases, this one provides popu­la­tion and demo­graphic inform­a­tion down to the “census block” level, which is the smal­lest unit of census geography.

These more detailed numbers have enough gran­u­lar­ity to enable map draw­ers to create districts that satisfy the consti­tu­tional require­ment that districts be roughly equal in popu­la­tion size. To comply with other legal require­ments, like the Voting Rights Act, states will have to consult addi­tional data, includ­ing estim­ates of citizen voting age popu­la­tion released as part of the bureau’s Amer­ican Community Survey.

The August 12 release of the redis­trict­ing data set follows the Census Bureau’s April 26 release of congres­sional appor­tion­ment data, which provided total head counts at the national and state level and was used to determ­ine the number of seats each state will have in the U.S. House of Repres­ent­at­ives for the coming decade. However, it didn’t include inform­a­tion about where people lived within a state or details about their age, race, and ethni­city, so it could­n’t be used to draw maps. (The bureau does not release inform­a­tion that iden­ti­fies specific indi­vidu­als, in keep­ing with legal confid­en­ti­al­ity protec­tions.)

Why are there two sets of redis­trict­ing numbers this year?

The Census Bureau is releas­ing two sets to enable states to get a head start on the redis­trict­ing process. The onset of the Covid-19 pandemic in 2020 just as the census count was getting under­way meant that the bureau has needed more time for collect­ing, processing, and releas­ing data.

To get results out as soon as possible, the August 12 numbers were released in what the bureau calls a “legacy format” — essen­tially an older, less user-friendly present­a­tion that may require mapmakers to do some addi­tional work sort­ing and organ­iz­ing the data before they can start draw­ing lines. The same redis­trict­ing data will be re-released in a more user-friendly format no later than Septem­ber 30. Crucially, while the August 12 and Septem­ber 30 data sets will be pack­aged differ­ently, they will contain the same numbers.

How long will it take for map draw­ers to be able to use the data released on August 12?

In most cases, it won’t take more than a couple of weeks. Although not all states will have the neces­sary resources to use the legacy format data set on their own, a number of them use third-party vendors who can. So, many states are expec­ted to start and poten­tially even complete their map-draw­ing processes before the user-friendly Septem­ber 30 data set is released.

What can these numbers tell us about the accur­acy of the 2020 Census?

Some things, but not everything. Assess­ing the qual­ity of the 2020 Census is a complex inquiry. The redis­trict­ing numbers offer some clues, but other partic­u­larly signi­fic­ant sources of inform­a­tion about census qual­ity are not yet avail­able.

Because the August 12 files provide gran­u­lar popu­la­tion and demo­graphic data at the local level, stake­hold­ers will be able to eval­u­ate them to see if the numbers match their sense of the loca­tion, size, and char­ac­ter­ist­ics of the communit­ies they know well. They can also compare the data files to other sources, such as recent sample-based surveys or demo­graphic projec­tions. These sources might help identify where under­counts or over­counts could have occurred, but the census numbers will still be the basis for line-draw­ing decisions. (Mapmakers, for instance, should not substi­tute the census for sample survey data, like data from the Amer­ican Community Survey, because those surveys are not actual popu­la­tion counts and do not provide the same level of gran­u­lar­ity as the redis­trict­ing data set.) The bureau has also commit­ted to produ­cing data qual­ity metrics over the course of the year that stake­hold­ers will likely scru­tin­ize for clues about how well or poorly the count went.

That said, the most import­ant and power­ful tool for analyz­ing the qual­ity of the count will be the bureau’s Post-Enumer­a­tion Survey (PES), It’s a survey collec­ted from a sample of house­holds that the bureau is running as an inde­pend­ent check against the 2020 Census results. The field­work for the PES is set to be complete by the end of the year, and it should, among other things, help identify under­counts of any specific racial or ethnic groups.

The bureau will not use the PES to adjust the appor­tion­ment or redis­trict­ing numbers — the survey isn’t designed to support those kinds of uses. But the inform­a­tion it should gener­ate will be import­ant for eval­u­at­ing whether polit­ical repres­ent­a­tion, fund­ing, and other govern­ment services reli­ant on census data are equit­ably distrib­uted. The initial results from the PES will be released in the first quarter of 2022, with addi­tional results to be released in the summer of 2022.