Skip Navigation

Why States Should Wait for Census Data to Draw Voting Districts

It would be a mistake to create new voting maps using the American Community Survey rather than the full 2020 Census results.

Anna Hoychuk

Every 10 years, states and local govern­ments redraw elect­oral districts to comply with the consti­tu­tional require­ment that districts must have roughly the same popu­la­tion. In redraw­ing maps, states and local­it­ies have long relied on redis­trict­ing data sets from the Census Bureau that break down the popu­la­tion to the “census block,” a small geographic unit about the size of a city block.

Under normal circum­stances, states would have received this block-level data by the end of March. But the Covid-19 pandemic required the Census Bureau to alter its oper­a­tions and the timeline for releas­ing popu­la­tion figures. Under the modi­fied sched­ule, the bureau plans to make redis­trict­ing data avail­able to states start­ing in August 2021.

Many states have or will need to adjust their redis­trict­ing dead­lines to accom­mod­ate this later date. Because of this timeline adjust­ment, a few states are consid­er­ing whether it might be possible to use altern­at­ive data sets, such as the Census Bureau’s Amer­ican Community Survey (ACS), to draw maps. Two states, Oklahoma and Illinois, have already done so.

But creat­ing final maps that are not based on census data would be ill-advised and expose states to litig­a­tion given signi­fic­ant differ­ences between census popu­la­tion data and ACS estim­ates.

How ACS data differs from census data

The ACS is an annual survey of around 2.5 percent of house­holds that is used to produce estim­ates about the char­ac­ter­ist­ics of Amer­ican communit­ies. It covers a broad array of topics, such as hous­ing, employ­ment, citizen­ship, race and ethni­city, and other demo­graphic inform­a­tion. The ACS plays a valu­able role in help­ing local offi­cials and resid­ents under­stand changes taking place in their communit­ies, and it influ­ences the annual alloc­a­tion of over $675 billion in federal and state funds.

By contrast, the census is charged once a decade with count­ing every­one living in the United States at the loca­tion where each person usually lives. The census asks a limited number of ques­tions about house­hold compos­i­tion, includ­ing the sex, age, and race of each person.

Equal­iz­ing district popu­la­tions during the redis­trict­ing process

Census data should be used to draw final redis­trict­ing maps because census data is based on an actual count of the U.S. popu­la­tion and provides greater geographic specificity and accur­acy than ACS data. ACS estim­ates, by contrast, are just that: estim­ates that come with the margins of error asso­ci­ated with any survey. That margin of error makes it hard to draw maps with the popu­la­tion preci­sion required by the Consti­tu­tion. Indeed, the Census Bureau itself says that the ACS is better suited to provid­ing demo­graphic inform­a­tion than total popu­la­tion figures.

Plus, as mentioned above, the smal­lest unit used for report­ing ACS data is signi­fic­antly larger than the units used to report census data. This also makes it more diffi­cult to use ACS data to satisfy the consti­tu­tional require­ment that districts have roughly the same number of people and at the same time satisfy other legal require­ments for redis­trict­ing. For these and other reas­ons, the Bren­nan Center joined Asian Amer­ic­ans Advan­cing Justice (AAJC), MALDEF, and over 50 other civil rights and good govern­ment organ­iz­a­tions in releas­ing a state­ment explain­ing why ACS data should not be used to draw final district maps. 

Appro­pri­ate redis­trict­ing uses for the ACS

Despite its unsuit­ab­il­ity for draw­ing legally compli­ant final maps, the ACS can be a very useful data source for Voting Rights Act (VRA) compli­ance and certain prelim­in­ary map-draw­ing tasks.

The VRA requires states to draw districts that give communit­ies of color an equal oppor­tun­ity to elect their candid­ates of choice. Part of that process involves look­ing to see whether partic­u­lar racial groups are suffi­ciently large to sustain districts. The ACS estim­ates demo­graphic char­ac­ter­ist­ics help­ful to making this determ­in­a­tion. But, even in this context, the ACS serves as just one compon­ent of a broader inquiry that relies on numer­ous data sources, includ­ing the census.

States can also use the ACS to prepare for redis­trict­ing while they wait to receive final census data. For example, the ACS can be used to identify areas with chan­ging popu­la­tions. It can also be a help­ful tool in defin­ing communit­ies of interest given the level of racial, ethnic, social, and economic detail that it provides. Using the ACS to help stream­line these prelim­in­ary tasks could make for a smoother redis­trict­ing process that produces fair maps once census data is avail­able.