Methodology

Where the ZIP codes come from

All ZIP code data on this site comes from the U.S. Census Bureau's relationship files, which map ZIP Code Tabulation Areas (ZCTAs) to state legislative districts.

What is a ZCTA?

A ZCTA (ZIP Code Tabulation Area) is the Census Bureau's approximation of a USPS ZIP code delivery area. ZCTAs are built from census blocks and are designed to closely match ZIP code boundaries. For practical purposes like ad targeting, ZCTAs and ZIP codes are interchangeable.

How districts are matched to ZIP codes

The Census Bureau publishes files that show where legislative districts and ZCTAs overlap geographically. If any part of a ZIP code area falls within a legislative district, that ZIP code is included in the district's list. This means a single ZIP code can appear in multiple districts when it straddles a boundary.

We intentionally include ZIP codes in all overlapping districts rather than assigning each ZIP to only one. This provides better reach for ad targeting, since you won't miss voters who live near a district boundary.

Data vintage

The current data uses 2024 state legislative district boundaries and 2020 ZCTA boundaries, as published by the Census Bureau. District boundaries reflect the latest redistricting cycle.

Limitations

• ZCTAs are approximations of USPS ZIP codes, not exact matches. Some ZIP codes used for PO boxes or unique delivery routes may not have a corresponding ZCTA.
• Boundary overlaps mean some ZIP codes appear in multiple districts. This is by design for ad targeting but may not be appropriate for every use case.
• Data is as current as the Census Bureau's latest release. If a state redistricts mid-decade, there may be a lag before updated data is available.

Source files

The raw Census Bureau relationship files used:

• House districts: tab20_sldl202420_zcta520_natl.txt
• Senate districts: tab20_sldu202420_zcta520_natl.txt

These files are available from the Census Bureau's geographic relationship files page.