Reimagining Redistricting 

Data Products

Emily Molfino, U.S. Census Bureau

Sallie Keller, U.S. Census Bureau

Any opinions and conclusions expressed herein are those of the authors and do not represent the views of 

the U.S. Census Bureau. The Census Bureau has reviewed this data product for unauthorized disclosure of 

confidential information and has approved the disclosure avoidance practices applied to this release.

DRAFT - For Internal Use Only
The Public Law (P.L.) 94-171 

dataset is created by the U.S. 

Census Bureau from the decennial 

census for use by the states in 

redistricting.

DRAFT - For Internal Use Only

Redistricting: The process of 

redrawing or redefining 

legislative district boundaries 

for federal, state, and local 

elections. 
DRAFT - For Internal Use Only

Federal 

requirements

Single Member 

Districts

Equal Protection

Section 2 of the 

Voting Rights Act

State Requirements (varies by state)

Compactness

Contiguity

Maintaining political subdivisions

Preserving communities of interest

Preservation of cores of prior districts

Avoiding pairing incumbents

Competitiveness
Fields in the P.L. 94-171 Data

• Race*

• Hispanic or Latino, and not Hispanic or Latino by Race* 

• Race* for the Population 18 Years and Over 

• Hispanic or Latino, and not Hispanic or Latino by Race* for the Population 

18 Years and Over 

• Group Quarters Population by Major Group Quarters Type 

• Occupancy Status (Housing) 

* Iterated for populations of one race and two/three/four/five/six races

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Over 300 

Fields!
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Geography
Uses Beyond Redistricting

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Population 

projections 

down to the 

county 

subdivision

Creating 

and/or 

analyzing 

Small-area 

Geographies

Prioritize 

Funding for 

activities

Health Policy 

Planning and 

Research

COVID 

Vaccination 

priority Areas

Group 

Quarter 

Population 

down to the 

CDP

Needs 

Assessments
Different Uses | Different Needs

DRAFT - For Internal Use Only

Redistricting

Other Uses
Disclosure and Confidentiality

1.5 billions statistics are released as part of the P.L. 94-171 data

DRAFT - For Internal Use Only

Wyoming California Rhode Island

53,769 Blocks 53,769 Blocks 25,649 Blocks

16,184,469 statistics 156,436,623 level statistics 7,720,349 level statistics

91% of statistics are 0 90% statistics are 0s 97% statistics are 0s

3% of statistics are 1 to 3 4% of statistics are 1 to 3 1% of statistics are 1 to 3
Thought Experiment

What if we could reimagine the geographic granularity of the 

P.L. 94-171 data that balances the various purposes and uses with 

privacy and confidentiality?

DRAFT - For Internal Use Only

Warning: This is an academic exercise only
Census Blocks are Not All the Same

8,129,271 blocks in 2020 

had some land

Median block: 0.4 km2

• Urban 0.02 km2

• Rural 1.1 km2

DRAFT - For Internal Use Only

Total Rural Urban

Zero Housing Units 27.7% 18.1% 9.5%

1-5 Housing Units 22.0% 16.4% 5.6%

6-10 Housing Units 12.5% 6.2% 6.4%

More than 10 Housing Units 37.8% 9.2% 28.6%

100% 100%

Zero People 29.1% 19.6% 9.5%

1-5 People 7.9% 6.6% 1.3%

6-10 People 8.5% 6.2% 2.3%

More than 10 People 54.6% 17.6% 37.0%

100% 100%
Congressional Districts

DRAFT - For Internal Use Only

Some misalignment with 

Tracts and Block Groups
State Upper Chamber

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More misalignment with 

Tracts and Block Groups
State Lower Chamber

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A lot more misalignment 

with Tracts and Block 

Groups
Police Service Areas

Wards Tracts

14

Still not perfect 

alignment.

Tract estimates are 

only available using 

5-year ACS data

Ward (county equivalent) 

is the lowest available 1-

year ACS data.

DRAFT - PRE-DECISIONAL
Chesapeake Bay Watershed

States County/Wards

15

Expands over 

three states Significant crossover across 

counties and wards.

Tracts

Some misalignment 

down to the Tract in DC.

DRAFT - PRE-DECISIONAL
Congressional 

and State 

Legislative 

Districts

Percent that Do Not Cross 

Congressional or Legislative Districts

Percent that Do Not Cross 

Congressional or Legislative Districts

DRAFT - PRE-DECISIONAL
Shifts across 

Time

Percent that Do Not Cross 

Congressional or Legislative Districts

Percent that Do Not Cross 

Congressional or Legislative Districts

DRAFT - PRE-DECISIONAL
Congressional, 

State 

Legislative, 

and Voting 

Districts

Percent that Do Not Cross 

Congressional or Legislative Districts

Percent that Do Not Cross 

Congressional or Legislative Districts

DRAFT - PRE-DECISIONAL
Gridded Data Product

Gridded data products are useful with:

• Longitudinal studies to avoid 

problems of changes to boundaries

• Comparatives studies to avoid 

mismatch between geographic 

concepts

• Studies that wish to examine larger 

customized areas with data that are 

not a standard Census Geography

Some uses of P.L. 94-171 data fall under 

this

BUT will present problems with redistricting.

DRAFT - For Internal Use Only
What does this tell us?

Redistricting

There are areas where the detail 

of blocks have not necessarily 

needed.... BUT this would not be 

known this in advanced.

Can this help inform future 

delimitation of blocks?

Other Uses

Larger areas might limit the 

utility in impacted areas, 

especially for small areas

Tract and block-group based new 

tools for aggregating to custom 

geographies using existing 

statistical products might be 

better suited

DRAFT - For Internal Use Only
Opportunities

Tailored statistical products, dissemination modalities, and tools for 

other uses of the P.L. 94-171 data

Other areas to explore:

• Adjustments to characteristics/content

• Synthetic Data

• Model Based Approaches

DRAFT - For Internal Use Only
Emily Molfino

Emily.Molfino@census.gov

DRAFT - For Internal Use Only
Voting 

Districts

Percent that Do Not Cross 

Congressional or Legislative Districts

Percent that Do Not Cross 

Congressional or Legislative Districts