How the data and the maps are made

The dataset is built precinct by precinct: 172,450 precincts in 50 states and DC, each with a boundary and its results. It covers general elections from 2016 through 2024 and the 2026 primaries, across 22 kinds of office from president down to the state legislature.

Boundaries. Some states publish a clean statewide precinct file; many leave it to counties, where a boundary might be a current shapefile, a PDF, a scanned map or a list of streets. Each one is found, digitized where it has to be, repaired, clipped to the coastline and checked for invalid geometry. The unit is the precinct as it is actually reported: where a county reports several precincts together, they are merged.

Results. 2026 results are pulled from county and state reporting, much of it PDF, parsed and matched to boundaries one county at a time, with anything automatic matching cannot settle checked by hand. Results from 2016 to 2024 come from VEST and the Redistricting Data Hub and are allocated onto the 2026 precinct boundaries, so every election can be compared on the same map.

Demographics. Race and population come from the 2020 Census; education, income, housing and age from the 2019–2023 American Community Survey. Both are aggregated from blocks into each precinct.

Metros. The hundred are the most populous metropolitan statistical areas (2020 Census definitions) in the dataset, the Census Bureau's core-based statistical areas of the metropolitan kind, by 2020 population summed from their precincts. Metro boundaries follow counties, and some counties are enormous, so each metro is drawn as a circle instead: centered on its population-weighted center, wide enough to take in 92% of its people, and never smaller than 20 miles plus 6.5 miles per square root of a million people, nor larger than 55. Every precinct the circle touches is drawn, clipped to its edge. The circle is only what is drawn: every total, margin and ranking covers all the precincts in the metro's counties. Density in the rankings is population-weighted, the density the typical resident lives at. The inset in the corner shows the metro's counties, its neighbors and state lines, with the circle dashed on top.

Margin. Each precinct is colored by its winner's share of all votes in the chosen year (2016, 2020 or 2024), in five-point steps from 50 to 95: Democrat, Republican, no votes recorded.

Shift. The change in two-party margin to 2024 from 2016 or from 2020, toward either party, on a scale set for each metro in steps of 2.5 or 5 points from zero.

Density. The margin colors, faded by that year's votes cast per square mile of the whole precinct, in five classes: under 50, 50–250, 250–1,000, 1,000–4,000 and over 4,000. Empty land fades into the basemap; dense neighborhoods stay solid.

On hover, each precinct shows its exact two-party margin or swing, to a tenth of a point. Roads are interstates and U.S. highways; city names are each metro's principal cities, placed downtown.

County clerks and state election offices; VEST and the Redistricting Data Hub for 2016–2024 results; the U.S. Census Bureau for boundaries of metros, counties and places, roads, and demographics; Wikidata for downtown locations. Map basemap © Esri, HERE, Garmin, OpenStreetMap contributors; page background © CARTO, OpenStreetMap contributors.

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