Why does a GPX file have no elevation data?

The short answer

A GPX track point only has to carry a latitude and a longitude. Elevation is an optional extra field, and a file is completely valid without it. When one arrives with no altitude at all, the cause is almost always upstream of the file itself: the device that recorded it had no altitude to give, or a tool that touched the file afterwards left it out.

The route on the map is unaffected either way. Distance, the shape of the line and the order of the points all come from latitude and longitude, none of which depend on elevation being present.

Where elevation lives inside the file, and why it is optional

Each recorded point sits inside its own track point tag, with lat and lon as required attributes. Elevation and a timestamp are separate, optional children nested inside that same point — present when the recorder had them to write, simply absent when it did not. GPX was designed in 2002 to exchange data between GPS devices from many manufacturers, and at the time plenty of receivers reported position only, with no altitude sensor behind them at all. Making elevation optional was the only way a file from one of those devices could still be a valid GPX file.

That history is still the reason the field is optional today, even though modern phones very often do have something to put in it.

The usual causes

• The recording device had no altitude source. Bare-bones GPS loggers and older receivers report a position and nothing about height, so nothing gets written for elevation because there is nothing to write.
• A route-simplifying or file-shrinking tool stripped it out. Editors that reduce a dense track down to fewer points sometimes drop elevation along with the points they remove, since the goal is a smaller file rather than a complete one.
• The file is a route, not a track. GPX distinguishes a track — what you actually walked, point by point — from a route, a smaller list of turn points meant to be followed rather than recorded. Routes are commonly built without elevation or timestamps at all, because neither one is the point of a route.
• The receiving service throws your elevation away on purpose. Some tools discard whatever altitude values arrive in the file and look up the terrain height at each coordinate in their own model instead. What you end up viewing is not missing elevation so much as elevation the service chose to replace, sometimes after the file itself has already been re-exported without it.

What actually gets lost without it

Elevation gain and loss cannot be computed from a file that has none, since both are built by walking through a sequence of altitude values and adding up the ups and downs between them. No values, no profile, and nothing to draw under the map.

Nothing else changes. Distance is the horizontal distance between consecutive coordinates, and pace is that distance over time, so both come out exactly as they would with elevation present. A GPX file with no altitude at all is still a completely usable record of where you went and how long it took.

How to check what a file actually has

GPX is plain text, so the fastest check is opening the file in any text editor and looking at a few track points: elevation, when present, sits as a short nested value right next to the timestamp on the same point. If none of the points have one, the file genuinely has no altitude data, and no amount of re-importing it elsewhere will make it appear. A flat, empty elevation chart in an app that normally draws one, on a route you know had real climbing in it, is the same signal seen from the other side.

What TrailCam does

TrailCam writes an elevation value for every point it can, since an iPhone reports altitude from GPS and, on most models, from a barometric sensor as well. A route recorded and exported straight from TrailCam carries elevation for the whole track, which is what the app draws as the climb profile under the map. Export is GPX 1.1, part of the optional TrailCam Pro upgrade; the app itself is free to download.