The distances shown on this site are computed from GPS coordinate data using the Haversine formula, which calculates the great-circle distance between consecutive points along the trail. These values will differ from the official Appalachian Trail Conservancy (ATC) figure of 2,197.9 miles for several reasons.
Point sampling. Any GPS track is a series of discrete points connected by straight lines. The real trail curves continuously, but the GPS data "cuts corners" between sample points. More points means better accuracy, but the computed distance will always be slightly less than the true distance.
2D vs 3D distance. The Haversine formula computes distance across the Earth's surface but does not account for elevation change. A steep climb or descent adds real distance that isn't captured. This site now incorporates elevation data to compute 3D distances (see below).
Trail reroutes. The AT is rerouted regularly. The GPS data may not reflect the most current path, and the official mileage is updated periodically by the ATC.
Measurement method. The ATC uses calibrated measuring wheels and field surveys. GPS-derived distances depend on receiver accuracy, satellite geometry, and post-processing methods.
| Source | Points | Computed Distance |
|---|---|---|
| ATC Official (2026) | — | 2,197.9 mi |
| NPS + SRTM Elevation (smoothed) | 690,117 | 2,198.3 mi |
| NPS ArcGIS (flat/2D only) | 690,117 | 2,161.7 mi |
| NPS + SRTM Elevation (raw) | 690,117 | 2,405.8 mi |
| at_centerline_full.gpx | 312,036 | 2,140.7 mi |
| the-entire-appalachian-trail.gpx | ~280,000 | 2,114.3 mi |
The pattern is clear: more data points and elevation awareness produce distances closer to the official figure.
This site computes 3D trail distance by combining the Haversine (horizontal) distance with elevation change between consecutive points:
distance = √(haversine² + Δelevation²)
Elevation data comes from SRTM (Shuttle Radar Topography Mission) via the Open-Elevation API, mapped to each of the 690,117 NPS trail vertices.
Smoothing. Raw SRTM data contains noise — small spurious elevation fluctuations between adjacent points that inflate the computed distance. A 32-point rolling average is applied to the elevation profile before distance calculation. This removes sensor noise while preserving real terrain features. The effect:
| Method | Distance | vs Official |
|---|---|---|
| Flat (Haversine only) | 2,161.7 mi | −1.6% |
| Raw elevation (no smoothing) | 2,405.8 mi | +9.5% |
| Smoothed elevation (window=32) | 2,198.3 mi | +0.02% |
This site uses the NPS ArcGIS Feature Service data (690,117 vertices) with SRTM elevation and a 32-point smoothing window for all distance calculations, including per-day leg distances, state section totals, and the completion estimate. The total trail distance computed from this data is 2,198.3 miles.
Hurricane Helene caused significant trail damage in Tennessee and Virginia. The NPS published official detour routes via the Helene_Detour_Route and APPA_HeleneStatusCenterline ArcGIS layers. This site incorporates those detours:
The detour routes are spliced into the trail centerline data, replacing the closed sections. Net effect: 2,161.7 → 2,163.7 mi (flat distance), approximately +2.0 miles.
Map overlay: Closed sections are shown as a solid orange line on the map. The full trail (including detours) is shown as a green line.
The trail centerline is rendered on the map as a green line. To balance download size with visual detail:
Static data (trail line, sections, elevation profile) is served in a content-hashed file (trail-static.[hash].js) that browsers cache indefinitely. Only the dynamic marker data (~185 KB) is re-downloaded on each visit.