Data & licences
What the answers are made of.
Every dataset and library behind the API, its licence, and the routes that use it. The rule: public-domain or permissively licensed sources only. This page is the audit trail for that rule.
Datasets
| Source | Licence | Used by |
|---|---|---|
| tz_world_mp Eric Muller, efele.net/maps/tz/world. Derived from VMAP0, a US National Geospatial-Intelligence Agency product. Frozen at tzdb 2016d. |
CC0 1.0 | GET /v1/timezone, the zone boundaries |
| IANA Time Zone Database Read at request time through the runtime's ICU, so offsets and DST rules are current without a redeploy. The test suite checks against zone1970.tab directly. |
Public domain | GET /v1/timezone, offsets, DST, abbreviations |
| TIGER/Line 2025 US Census Bureau. Full-resolution county and 119th Congress district files. Unlike the generalized cartographic boundaries, these include legal water area, so harbours and offshore coordinates land in a county. |
Public domain, 17 U.S.C. §105 | GET /v1/us/geographies |
| EPSG Geodetic Parameter Dataset © IOGP. Coordinate reference system definitions, exported through PROJ 9.5. Codes are used unaltered, as the EPSG terms of use require. |
EPSG terms of use | POST /v1/transform, the State Plane and NAD83 UTM definitions |
| Census Geocoder Used in tests only. The independent authority 650 coordinates were checked against before /v1/us/geographies was believed. |
Public domain | Tests only |
Elevation (USGS 3DEP, Copernicus GLO-30) and NOAA chart products are planned. Copernicus data carries an attribution requirement, and its row will be added here the day that route ships.
Libraries
| Library | Licence | Used by |
|---|---|---|
| H3 (h3-js 4.5) Uber's hexagonal hierarchical index. Compiled to asm.js, which is why it runs on Workers. | Apache 2.0 | /v1/h3/*, and the indexes behind both lookups |
| proj4js 2.21 Accuracy is verified against PROJ 9.5, because proj4js answers Infinity for a position outside a projection's domain instead of throwing. | MIT | /v1/transform |
| Turf 7.4, scoped packages With ellipsoidal corrections applied on top: turf's buffer and area are spherical, and the route descriptions say by how much. | MIT | /v1/geometry/*, /v1/geojson/*, /v1/pip |
| JSTS 2.7 The overlay engine under turf's buffer, union, intersect and difference. | EPL 1.0 or EDL 1.0 | /v1/geometry/* |
| Hono | MIT | Routing |
| @x402/hono, @x402/core | Apache 2.0 | Payment middleware |
| Fraunces, IBM Plex | SIL OFL 1.1 | This site |
Why public domain only
Licensing is the margin killer in this market, so the API sells computation and public-domain data and carries nothing with redistribution terms. The timezone route is where that rule first cost something, and the reasoning is written down here.
The obvious timezone dataset is timezone-boundary-builder: current, accurate, 419 zones. Its code is MIT and its output data is ODbL 1.0, and the two licences sit in separate files so a licence badge reads MIT. Reading the OpenStreetMap Foundation's guidelines carefully, individual API responses are probably fine. Three obligations still attach, and this project declines to carry them: attribution on public use, a standing duty to hand any requester a machine-readable copy of the derivative database free of charge, and share-alike on the derivative the moment the geometry is reshaped. Reindexing polygons into an H3 grid is reshaping, and OSMF has no guideline on indexing. This project declines to rest a paid product on an open question in the licensor's wiki.
So /v1/timezone uses tz_world_mp, CC0, derived from a US government work. It is frozen in 2016, and what that costs is measured and stated in the route description: of the 312 principal locations in IANA's zone1970.tab, 293 resolve to the right zone, and the four regions that split after 2016 are named. The staleness was the price of the licence, and it was paid deliberately.
Several npm timezone packages ship that ODbL data under an MIT label and pass a naive SBOM scan. This project builds its own CC0 index instead.
Attribution we owe
Of the sources above, only the EPSG dataset asks for anything: that codes stay unaltered and that the dataset be credited, which the table does. The Census Bureau and NGA products are US government works, efele.net's map is CC0, and IANA's database is public domain. This page exists because a buyer deciding whether to trust a coordinate lookup is entitled to know where the boundaries came from and how old they are.