About the data
What to check before you key up
- The boundary. Use the park's official map (the "Park website" link on a park page) or pota.app to confirm you are inside the park. Our shapes are a guide to where the park probably is.
- N-fer spots. An overlap drawn here means two shapes intersect in our data — it does not mean the land is inside both parks in reality. Trail corridors in particular are often a few metres wide in OSM and much wider (or narrower) on the ground. Confirm you are inside every reference you plan to claim.
- Parking. Lots and trailheads come from OpenStreetMap and may be closed, seasonal, or private. Check signage.
Where the shapes come from
Park locations and counts come from pota.app, which stores one point per park. The lines and polygons come from OpenStreetMap: for each park we look for a named route relation (trails) or protected-area boundary (parks, forests, refuges) whose name matches the pota.app name and which sits near its marker. The match is by name similarity, so typos on either side, a renamed trail, or two parks with similar names can pick the wrong shape or none at all.
OpenStreetMap has no outline for most state wildlife management areas, BLM units and conservation areas, so park polygons also come from the USGS Protected Areas Database (PAD-US), the public-domain national inventory of protected land. Each park page says which source its shape came from. PAD-US boundaries are compiled from state and federal agencies and are usually the better outline, but they are a database of ownership and management, not a survey: parcels can be stale, and a unit's name in PAD-US may differ from pota.app's.
Every shape carries a confidence (how well the name and position agreed) and a verified flag. "Unverified" means nobody has checked it by hand; "verified by staff" means a person looked at it and confirmed or corrected it. Parks with no shape at all show as "marker only" and are treated as their pota.app point.
N-fer zones are computed by intersecting those shapes. They inherit every error in the shapes they came from, and OSM's trail lines are usually the centreline, not the corridor.
How to fix a bad shape
Use "Something wrong?" on the park page. Reports go straight to the maintainer's queue, and corrected shapes are marked verified so a future re-match cannot undo them. Better still, fix the name or boundary in OpenStreetMap itself — the next monthly refresh picks it up, and every other map benefits.