This article explains what population projection are, and answers questions about why these datasets are useful for redistricting, what is included in the data, and how it was processed.
Population projections estimate populations at future dates. They help us answer questions about the predicted demographic makeup of a particular geography in the near future.
Population projections can be calculated at different geographic levels and for different racial or ethnic groups. Populations can also be projected out for any number of years. Projections are used not only in redistricting, but for academic research and planning purposes across a variety of sectors, include “get out the count” work related to the census.
Census Block-level projections can be used to measure the impact of a proposed redistricting plan over a ten year period. A related use of Census Block-level population projections is in drawing districts that minimize demographic and total population changes between districts over a ten year period.
They may also be used in Racially Polarized Voting (RPV) litigation to predict what districts will look like in future elections.
HaystaqDNA projections are available at the census block and block group levels, and include projections for the total population, and the total population by race/ethnicity. These files are available in both CSV and SHP formats.
RDH projections are available at the census block and county levels, and include projections for the total population and the voting age population (VAP), both broken down by race/ethnicity. Note that the racial VAP categories include both Hispanic and non-Hispanic, whereas the total population projections are for “non-Hispanic race alone” (and exclude those who also identify as Hispanic). These files are available in CSV format.
Projections for a single block should be viewed with caution. We provide block level projections so that users can aggregate the data to larger geographies, such as districts.
You can use our dashboard to easily access the RDH projections at the county, state legislative and congressional district levels.
We host two sets of projections. The first set of projections was created by HaystaqDNA in 2021, using the 2010 decennial census and 5-year American Community Survey (ACS) estimates from 2019 to project the population annually from 2020 through 2030. The second set of projections was created by RDH in 2025, using the 2020 decennial census and the 5-year ACS estimates from 2023 to project the population annually through 2035.
Both projections generally estimate rates of population change for the total population and the population by race/ethnicity by calculating a rate of change between the two years of data.
HaystaqDNA aggregated 2010 Census Block data up to the Block Group level. Then, they estimated rates of population change based on the racial and ethnic makeup of the Block group. Next, they used geocoded voter file and commercial file data to identify areas of new development, such as housing developments that did not exist during the 2010 census, and calculated a rate of change for those areas. Last, they disaggregated the population projections back down to the Block level.
RDH’s methodology is slightly different for total population and VAP projections. Both datasets start by aggregating the data up to the county level, to calculate a county-level rate of change. A rate of change was also calculated at the block group and tract levels for total population and VAP, respectively. Projections are based on a weighted average of these two rates of change, with caps placed on growth that are relative to the size of the population in that geography, so that smaller populations receive lower caps on growth and depend more heavily on the rate of change at the county level.
RDH projections were calibrated against statewide projections provided by the University of Virginia’s Cooper Center for Public Service. VAP projections were thresholded to be between 65 and 90% of the total population projections. A final adjustment was made to all projections to ensure horizontal integration, so that the sum of all racial/ethnic groups within a geography equal the total for that geography.
For more details on methodology, view the metadata for the dataset you are downloading.
Population projections can be found on each state’s data download page. Go to statewide data downloads and select “Projections” in the “Filter by Type of Data” dropdown menu.
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