Sources
Every figure on this site traces back to an official government source, refreshed daily. Nothing here is crowdsourced, inferred, or filled in where the record is silent.
The population half of the arithmetic does rest on a survey, and says so: the Census Bureau’s American Community Survey is the official count of who lives where, and it is an estimate with a margin of error like any survey. What this site does not do is add estimates of its own on top of it.
Data sources
The Library of Congress’s official API for bill text, sponsors, CRS summaries, and House roll-call votes from the 115th Congress (2017) forward.
The Clerk’s own roll-call XML archive, used to reach House votes from before api.congress.gov’s coverage begins: the same official record, reached a different way for years the modern API doesn’t expose.
The Senate’s own roll-call XML archive, back to 1989. api.congress.gov has no Senate vote endpoint, so this is the official record read directly rather than through a third-party mirror.
Census Bureau, American Community Survey
Voting-age population by congressional district and by state. Each vote uses the ACS one-year estimates published for the year it was cast, which is the release that was current at the time. Where no one-year release exists for a year, the five-year estimates covering it are used instead: the Census Bureau did not publish standard one-year estimates for 2020, so votes from that year are the exception. Every measure page names the exact release its own figures came from. See the Methodology page for how this basis is defined and why the dataset starts in 2005.
unitedstates/congress-legislators
A community-maintained, open-source roster of every member of Congress, including historical members who have since left office, used to map each vote to a district or state.
Licensing and attribution
Roll-call votes, bill text, CRS bill summaries, and Census population data are all works of the U.S. federal government and are in the public domain in the United States (17 U.S.C. § 105). Bill descriptions on this site are trimmed verbatim from official CRS summaries, never rewritten, per the strictly nonpartisan house style described on the Methodology page.
The unitedstates/congress-legislators project is open source under the CC0 public-domain dedication.
This site’s typefaces (Libre Caslon Display, Libre Caslon Text, IBM Plex Mono, and Caveat) are Google Fonts, each licensed under the SIL Open Font License 1.1. The share-card image generator vendors its own static copies of Google Fonts under the same license, so that route keeps working without a live request to Google Fonts during high-traffic moments.
Every chart, bar, and illustration on this site is original, hand-built SVG or CSS: no stock imagery, icon library, or third-party chart library is used anywhere.