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Credits and data sources

Cairn is free and stores nothing. It is a window onto data that other people publish. They did the hard part, so here is who to thank and whose terms apply to what you download.

Boundaries

U.S. Census Bureau, TIGERweb. ZIP code areas (ZCTAs), state legislative and congressional districts, counties, cities and towns, school districts and census tracts. Public domain. ZIP areas are Census approximations, not official USPS delivery boundaries. This product uses Census Bureau data but is not endorsed or certified by the Census Bureau.

Verified sources

National Interagency Fire Center (WFIGS). Wildfire perimeters and locations. Do not use for decisions about life or safety; follow local officials.
U.S. Geological Survey. Earthquake feeds. Public domain.
National Park Service, Land Resources Division. Park unit boundaries.
USDA Forest Service. National forest boundaries and trails.
FEMA, National Flood Hazard Layer. Flood hazard zones. Not a substitute for an official flood determination.
NOAA National Weather Service. Active watches, warnings and advisories.
DeFlock (deflock.org) and OpenStreetMap contributors. Locations of license plate reader cameras, under the Open Database License.

Marathon courses

Each course belongs to its race organizer, and each result in Cairn names where its copy came from and what year it shows. Courses change from year to year, so check the organizer's own map before race day.
Denver Colfax Marathon. Course, water stations, mile markers and medical stations from the organizer's 2026 course map (RaceJoy).
Los Angeles Marathon. Los Angeles County Department of Health Services.
Marine Corps Marathon. Marine Corps Marathon Organization, U.S. Marine Corps.
Oklahoma City Memorial Marathon. City of Oklahoma City.
Chicago Marathon. Esri sample data.
Twin Cities Marathon. A University of Minnesota student project (2014 course).
St. George Marathon (City of St. George) and Anchorage Mayor's Marathon (Municipality of Anchorage).
Boston, New York City, Miami, Houston, Honolulu and Philadelphia are traced by Cairn: drawn along OpenStreetMap roads from each organizer's published course, then checked against 26.2 miles. They follow the right streets but are approximate, and their mile markers are estimates. Houston's refueling stations are read off the organizer's 2026 map and are within a few blocks, not exact.
If you organize one of these races and want a course updated or removed, open an issue on GitHub.

Everything else you find by searching

ArcGIS Online search, by Esri. Each result belongs to the city, county, agency or person who published it. Use the Source link on a result to read its terms before you reuse the data. Cairn shows the publisher's copyright note when one is provided.

The map and place search

Map drawn with MapLibre GL JS. Fonts: Noto Sans and Schibsted Grotesk.
Address search by Esri's geocoding service and OpenStreetMap Nominatim. Searches are sent only when you press Go and are never stored by Cairn.
Directions by the open routing servers run by FOSSGIS (OSRM, with Valhalla as a backup), or by OpenRouteService from HeiGIT. Route data © OpenStreetMap contributors.
Airport locations from OurAirports, public domain.

Cairn itself

Made by Robert Youshock. Code is open source under the MIT License: github.com/robertyoushock/cairn.
No accounts, no ads, no tracking. Your list lives only in your browser tab.
Found a wrong label or a dead layer? Use "Report it" on any result, or open an issue on GitHub.