About Trailmonger

Trailmonger is an offline adventure-mapping app for iPhone, iPad, Android and the browser. One map for hiking, hunting, fishing, paddling, mountain biking, running and off-roading, built so that it keeps working after the signal stops.

Today it covers 164,667 named trails and 399,659 miles across 2,122 counties in 51 states and territories. Those figures are read from the live map data each time this page is built; they were last recomputed on 2026-09-02.

Why it works offline

Most mapping apps cache pictures of the map you already looked at. Pan somewhere new with no signal and you get grey squares, because the picture for that square was never downloaded. It is the failure mode that shows up exactly when you need the map most.

Trailmonger downloads the underlying vector data instead — the roads, trails, contours and labels as geometry rather than as images. The map stays searchable, zoomable and routable in places you have never opened before, because the device is drawing the map rather than fetching a photo of it. Routing runs on the device too, so you can plan a way out without a connection.

How the map is built

Trailmonger is assembled from public and open data rather than licensed wholesale from a single vendor. Trail geometry comes from OpenStreetMap. Elevation and terrain come from the USGS 3D Elevation Program, hydrography from the 3D Hydrography Program, water levels from USGS stream gauges, tides and bathymetry from NOAA, and public-land and hunt-unit boundaries from the federal and state agencies that publish them. Property parcel data is imported per state, from 45 states so far.

It is rebuilt on a schedule, not scraped once and left: points of interest daily, the trail network every Sunday, boundaries every Monday. Because trails come from OpenStreetMap, correcting an error at the source corrects it here within the week — and that fix helps everyone using OSM, not just us. Every layer’s actual age is published on our data freshness page, and the full source list with licences is on data credits.

What we publish back

Building on open data carries an obligation to return something. We publish trail coverage aggregates for every state and every published county — named trail counts, mileage, activity splits and mapped points of interest — as CSV and JSON on our open data page, under the Open Database Licence, free to republish with credit. Researchers, journalists and parks departments are the intended audience, and no attribution deal or API key is required.

We also publish what we cannot republish, and why. Property parcels are excluded because several states legally bar redistributing them — Georgia requires a resale restriction, South Carolina makes commercial use of owner names a misdemeanour, Washington holds the records confidential. State hunt-unit boundaries are excluded pending a per-agency review, because permission to display data in an app is not permission to hand out copies of it. Quietly omitting those would have been easier than explaining them; we would rather you know where the edges are.

What it costs

The app is free to download, and the things that matter when something goes wrong are free with it: offline maps, recording, and the safety and location-sharing features. A paid tier adds property parcels and the premium map layers. We would rather someone who has not paid us still have a working map and a way to call for help.

Who builds it

Trailmonger is independently built and actively maintained in the United States. It is not a re-skin of someone else’s map product — the data pipeline, the tile infrastructure, the routing engine and the apps are all run in-house, which is why the rebuild cadence and per-layer dates above can be published at all.

Support email reaches the people who build it. If something on the map is wrong, say so: support@trailmonger.com. Reporters and directory editors will find boilerplate, figures and logos on the press page.