Reducing a GPX file that's too heavy for a GPS unit

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.

Setting the tolerance and checking before you export

The higher the tolerance, the lighter the file gets, but the greater the risk of cutting a tight bend. Good practice is to raise the tolerance gradually, watching the simplified track overlay the original, until you reach a level that meaningfully shrinks the file with no visible gap on the technical sections.

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.