Reducing a GPX file that's too heavy for a GPS unit
A GPS unit that lags or refuses to load a track usually has just one problem: too many points for what it can handle.
The symptom: a unit that refuses to load
A GPX file that takes an unusually long time to open, or that a GPS unit flatly refuses to load, is almost always suffering from the same problem: too many points relative to what the device can handle.
Why a file gets too heavy
Older-generation Garmin Edge units, entry-level GPS watches and some Wahoo devices set a points-per-file limit. A long recording — an ultra, a multi-day hike, a cycling tour — can pass 50,000 points and cross that limit without warning, right up until loading fails on the ground. File size in kilobytes tracks the point count directly: a GPX file is just a list of coordinates repeated point by point, with no compression — twice the points means twice the size.
Simplifying without distorting the track
Cutting down the point count shouldn't distort the track. That's the job of the Douglas-Peucker algorithm: it removes points that add no information about the track's shape — typically ones sitting on a straight line — and keeps the ones that mark a genuine change of direction, like bends.
A slider sets the tolerance in metres, and a counter shows how many points will be kept before you confirm. On a watch recording, a tolerance of 5 to 10 m often removes more than 80% of the points with no visible distortion at map scale. A wrong step can be undone with Undo (Ctrl+Z).
📖 Step by step in the manual: Simplify · Clean up GPS spikes
Setting the tolerance and checking before you export
The higher the tolerance, the lighter the file, but the greater the risk of cutting a tight bend. Good practice is to start with a low tolerance, apply it, look at the technical sections on the map, then try one notch higher if the file is still too heavy. If a tight bend has been cut, Undo brings back the previous track.
The most common mistake: simplifying too hard, all at once
Applying a high tolerance straight away to save weight quickly tends to cut the tight switchbacks of a mountain road or the twists of a technical trail — exactly the places where the track's precision matters most. It's better to start from a low tolerance and raise it in steps, checking at each stage that the route's most winding sections stay faithful to the original.
What about a track that's already had its elevation corrected
Simplification acts on the point count, not on already-corrected elevation values — the two operations are independent and can happen in whichever order suits, without one undoing the other's work.
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