Some Common Questions (And Answers!) On The Census

Amidst mid-decade redistricting, and recent discussions about the Census, we wanted to provide some common questions, and answers, about redistricting and census data.

What is the census?

The United States census is a once-a-decade project conducted by the U.S. Census Bureau to count every resident of the United States. The decennial census is mandated by the U.S. Constitution and federal law, and is the largest peacetime federal activity conducted by the government.

In addition to the decennial census, the U.S. Census Bureau, a non-partisan statistical agency within the federal government, conducts many other scientific surveys, including the American Community Survey (ACS), as well as other projects to gather important demographic information used by researchers, employers, and policymakers. 

How and when is census data released? 

Following the decennial census, which occurs in years ending in -0, the Census Bureau releases data in years ending in -1. 

Who is counted in the decennial census?

The U.S. Constitution requires that the decennial census count everyone in the United States. While political actors have attempted to target and exclude specific groups, such as individuals on temporary visas or undocumented residents, the Constitution’s mandate is clear that the decennial census must reflect the total number of all persons residing in the United States. 

How is census data protected?

The data collected in the decennial census is designed for statistical purposes— not to gather information about individuals. Federal law prevents the disclosure of any information that could be traced back to an individual person, with severe criminal penalties for any violation. Moreover, federal law prevents any information the Census Bureau collects from being used against an individual by another federal agency.

Prior to the release of decennial census data, the Census Bureau puts the data through a rigorous disclosure avoidance process to ensure the data is fully anonymized and cannot be traced back to any individual person.

The Census Bureau’s data remains the most reliable measure of where residents live and who they are. It is important to maintain the integrity and privacy of census data to ensure that it can continue to serve its critical functions, including being a critical building block of redistricting and representation in this country.

How does the census relate to redistricting?

The decennial census provides the population data necessary to ensure that districts have equal populations.

After a new decennial census, we have an updated snapshot of population changes across the states. Some states and areas gain population and therefore gain new districts through apportionment, while other states lose residents and possibly lose districts as well. The total number of congressional seats across the country must first be allocated among the states – through a process called apportionment –  then the states must redraw their districts to ensure each district has roughly the same population.

This concept of “one person-one vote” was established by a series of U.S. Supreme Court decisions beginning in the 1960s, as the Court determined that, under the U.S. Constitution, congressional districts within states must be as equal in population as possible. As a result, congressional districts within each state can only have a population deviation of plus or minus one person. In other words, each district can only contain one more person, or one less person, than any other district in that state. With the publication of new decennial census data, states must rebalance their congressional districts to the new ideal population size.

Map drawers have more flexibility with state legislative maps. Population equality requirements for legislative maps vary by state, but state legislative districts may generally vary by plus or minus 5% of the district’s population. In practice, this means the largest state legislative district could be 10% bigger than the smallest state legislative district in the state by population.