Altigraph · GPX elevation profile

The elevation profile of a GPX file: climbing, gradients, how to read it

A GPX file holds the track of a route and, almost always, the altitude of every point. The elevation profile is the curve drawn from it: distance along the bottom, altitude up the side. It tells you where it will hurt, where you can push again, and how many metres you will climb in total.

Where to find the GPX of a race

• The athlete guide or the organiser's website: most races publish the course as a GPX, or as a Strava link. If it is a Strava link and you have no account, it can still be read without one.
• Strava: on a route (not an activity), the "..." menu offers "Export GPX". On an activity, the same export sits in the activity menu.
• Garmin Connect: on a course or an activity, the gear icon at the top right offers "Export to GPX" (and "Export Original" for the FIT file, which Altigraph reads too).
• Komoot, Ride with GPS, AllTrails, Outdooractive: every route has a GPX export button, sometimes reserved to free accounts.

How climbing is computed, and why it differs from one tool to the next

Total climbing (elevation gain, D+) is the sum of every uphill metre. The catch: the altitude reported by a GPS watch wobbles by a few metres from one point to the next, even on the flat. Add every little jump and the total inflates. So every tool smooths the curve before adding, and each smooths its own way: that is why Strava, your watch and the race website never quote exactly the same figure.

Altigraph resamples the track every 10 m, smooths the altitude over 50 m either side of each point, then adds the ups. That setting removes GPS jitter without flattening a real bump. It usually lands 5 to 10 % below the figure quoted by race organisers, who smooth less or not at all. When the Strava distance is known, it is shown next to the computed one for comparison.

There are three sources of altitude, and they are not equal: GPS altitude (the least accurate, far more than the position on the map), barometric altitude from recent watches (steadier, but it drifts with the weather) and "corrected" altitude from a terrain model, which Strava or Garmin apply afterwards. A GPX exported from a route drawn online carries terrain-model altitudes, smooth and consistent; a GPX recorded by a watch carries the sensor's.

Reading a gradient in percent

An 8 % gradient means 8 m gained for every 100 m travelled. Over 1.2 km at 8 % you climb 96 m. Percent is not an angle: 100 % is 45 degrees, not a vertical wall.

Two figures matter when preparing a race, and the profile alone shows only one: the average gradient of a climb tells the overall effort, the peak (the steepest 100 m) tells whether there is a wall in the middle. A climb averaging 5 % with a 14 % peak is not run like a steady 5 % climb. That is why Altigraph cuts the route into sections and gives both: the average and the steepest 100 m, with the kilometre where it sits.

How the cut is made: the local gradient is measured over a sliding 100 m, every point is classed as climb (over 1.5 %), descent (under -1.5 %) or flat, and pieces shorter than 150 m are merged into their neighbours so the profile is not chopped up. The table only keeps the sections that weigh: longer than 200 m at 2 % or more, or at least 10 m of elevation change.

What you get when you drop the file

1. The profile coloured by gradient (orange climbs, blue descents), with km, altitude and gradient under the mouse or the finger.
2. The table of sections: from where to where, length, start and end altitude, average gradient, steepest 100 m.
3. The steepest stretches over 100, 250, 500 and 1,000 m, uphill and downhill.
4. The map, with the track coloured by gradient.
5. A 1600 x 900 image to send to your group and a link that replays the profile: the profile is compressed inside the link itself, no server keeps your file.

The cases that get stuck

• No altitude in the file: some tools export a track without altitude tags. Altigraph says so; export again from a service that adds altitudes (Strava, Komoot and Garmin Connect always do).
• Several tracks in one GPX: the longest is shown, and the page says so, rather than drawing a straight line between two pieces.
• A FIT or TCX file instead of a GPX: the three formats are dropped the same way.
• A very large file (a ride of several hundred kilometres): everything is computed in your browser, allow a few seconds.

Published 19 September 2026. The thresholds quoted (10 m, 50 m, 100 m, 1.5 %, 150 m, 200 m, 2 %) are those of Altigraph's own computation, also described in the questions on the home page.