ZIP Code Boundary Map Demo — Overlay Counties, Cities & Districts

Sample extract

Download this extract

All eight formats, the documentation, and a context/ folder with the overlay layers as GeoJSON.

Overlay a geography

Display

ZIP fill 35%

Name the overlays

The map library and the first extract are about a megabyte together, so they are not fetched until you ask for them.

Load the map

Free to explore — no signup, nothing to install.

Click a ZIP Code on the map. You will get every attribute that ships in the file, and the counties, cities, districts and tracts it actually overlaps — with the share of the ZIP each one covers.

Every ZIP Code in the country, the same way

What you are clicking is 197 of them. The licensed file carries ~32,000 polygons and ~41,000 centroids, in all eight formats, with every quarterly rebuild for the license term. You can also buy just the part you need.

$5 per ZIP Code · up to 65
$645 a single state
$1,290 nationwide, one user

Price it for your project Take a free extract first

ZIP Code boundaries are drawn as black polygons; the other geographic areas are context, each in its own colour. The ZIP Code boundaries are the exact bytes from the downloadable sample archive, at full precision. The county, city, district and tract layers are Census cartographic boundaries, generalised for display so the page stays quick — they are here to show relationships, not to be measured against. The overlap percentages in the right-hand rail were computed on the full-precision geometry of both, not on what you see drawn.

What you are looking at

Six things worth knowing before you judge the data by the picture.

These are carrier routes, not ZCTAs

The polygons come from USPS carrier route geography — the actual walk and drive sequences a letter carrier serves — rebuilt every quarter. Census ZCTAs are built the other way round: block groups aggregated to whichever ZIP appears most on their addresses, once a decade.

Switch on Census tract and the difference stops being an argument. ZIP edges cut through tracts constantly, because one follows delivery and the other follows population.

The red dots are ZIP Codes too

A PO Box ZIP and a Unique ZIP assigned to one building have no delivery area to draw. They are real ZIP Codes that will appear in your address data, so the file ships them as points rather than pretending they have shape.

Military ZIP Codes have no area either — and they are not in this product at all. They live in the ZIP Code Database and ZIP+4 instead, with every attribute except a shape.

In the LA Metro extract that is 196 of 498 records. Any workflow that only reads polygons drops every one of them silently — which is exactly the bug this map is designed to make visible.

A ZIP Code is not a city

Switch on Place and click almost anything. The NAME attribute is the preferred mailing name the USPS assigns, not a municipal boundary — so a ZIP labelled for one city routinely covers slices of three or four others, and stops well short of the city limits.

The percentages in the rail are the honest version of that relationship: the share of the ZIP’s area inside each place, largest first.

How the percentages are computed

For every ZIP with an area, the intersection of the ZIP polygon and each overlapping geography is measured, then divided by the ZIP’s own area. Same maths the internal tool runs, on the same geometry — the results were just written to a file instead of returned to a browser.

Point ZIP Codes have no area to divide by, so they report within rather than a fabricated 100%. A percentage nobody can compute is not a percentage.

Multipart shapes, and one GeoJSON gotcha

Plenty of ZIP Codes are more than one piece — an island, a parcel across a river, a patch on the far side of a park. Those arrive as multipart geometry, and this page folds any GeometryCollection in the sample into a MultiPolygon before drawing, because MapLibre and Mapbox GL will not render a collection at all.

If you load our GeoJSON into a web map and a handful of ZIP Codes are missing, that is almost always why — and it is a one-line fix, not a data problem.

Coordinates and precision

WGS84, SRID 4326, longitude before latitude, per RFC 7946. Nothing to reproject for PostGIS, SQL Server, ArcGIS, QGIS or any browser map.

The product ships at six decimal places — roughly 11 cm. The context layers on this page were deliberately thinned for the browser; the file you buy never is.

How our experts use this

The percentages in the right-hand rail are not a feature of this page — they are what our ZIP Code API computes, and this map is the view we run on it. The API is built on these boundaries rather than a table of midpoints, which is why it can answer questions a lookup service cannot.

A coordinate resolves to everything containing it Pass lat,lon where a ZIP Code would go and you get the ZIP whose delivery area contains that point — plus the county, place, CBSA, Census tract and block group it falls inside. Filler polygons are included, so a point in open country still resolves.
A radius that measures area, not midpoints Two modes. centroid is the usual thing: a ZIP is in or out depending on where its midpoint lands, so a ZIP clipped by the edge of the circle is either counted whole or missed entirely. spatial intersects the actual polygons and returns pct_inside for every ZIP — the fraction that is genuinely in range.
Demographics that respect that fraction The overlap share carries into the ACS aggregates the same call returns, so the ZIP Codes around the rim of your circle are weighted by how much of them you actually asked for. Count whole ZIP Codes instead and every partial one on the edge is overstated — on a small radius that is most of your answer.
The crosswalk on this page, as a response Counties, places, CBSAs, Census tracts and block groups for any ZIP Code, each with the share of the ZIP it covers. Same computation as the rail, against live geometry rather than the four extracts frozen here.

One thing the API does not do: it never returns the polygon. You get coordinates, bounding boxes and overlap shares — the geometry itself only comes in the file. If you need shapes to draw, buy the boundaries; if you need answers about shapes, call the API.

The file and the API are the same data. Buy the file when you want it in your own database; call the API when you want the answer without keeping the data at all.

See the API Price the file

Take the files with you

Every extract on this map is a free download, in all eight formats, with the product documentation in the archive. Each one also carries a context/ folder holding the overlay layers you have been switching on, as GeoJSON.