When you record your activity using AllTrails, we use your lat/long to lookup elevation for each point in your activity because phones are generally bad at keeping track of elevation.
While this approach improves accuracy in almost all cases, there are two challenges specifically when you are in a canyon:
- GPS hardware gets confused in canyons because the signals bounce off the walls, so horizontal accuracy at the device level is often bad.
- There can be a lot of elevation change over a small horizontal distance, so a small inaccuracy in lat/long can translate to a large inaccuracy in elevation.
Essentially, you will sometimes get elevation values from the top of the canyon wall rather than from the floor of the canyon where you're actually hiking. Please be aware that this can throw off the elevation graph and elevation gain calculations for activity recordings taken in canyons.
When you upload GPX files, the “Smooth GPX” checkbox will be selected by default to minimize this issue. Activities taken with the AllTrails app are already smoothed so any AllTrails GPX will not be re-smoothed on import regardless of the state of the checkbox.