A GPX track can look completely fine on a map — a clean line following a route — and still have problems that only show up once you look point-to-point instead of at the shape as a whole. A duplicate GPS fix, a clock that jumped backward, or one bad reading that implies teleportation don't bend the line in a way you'd notice by eye, but they'll throw off a pace calculation, a duration, or an elevation-gain total computed from the same data.
The four things worth checking
A point that exactly repeats the one before it. GPS loggers write this fairly often — the same fix recorded twice in a row. Harmless to look at, but it inflates a point count and, depending on how a downstream tool handles zero-distance segments, can quietly break a pace calculation.
A timestamp earlier than the previous point's. This one is a genuine impossibility for a single recorded track — a clock jump, or two logs merged out of order — and it breaks anything computing duration or pace across that pair, since "seconds elapsed" briefly goes negative.
A gap of several minutes between consecutive points. Usually completely legitimate — a rest stop, a phone put away mid-hike — but worth knowing about, since some analyses (average pace across the whole track, for instance) treat a gap the same as continuous movement unless you account for it.
A speed between two points that isn't physically plausible. If the implied speed between one fix and the next is faster than a few hundred kilometers an hour, that's not real movement — it's almost always a single bad GPS fix, sometimes paired with a clock issue, and it's the kind of single outlier that can badly skew an average-speed or total-distance figure computed naively.
What gets fixed automatically, and what doesn't
The GPX Cleaner removes exact duplicate points automatically when you ask it to, because that's the one fix here that can't lose information — a point at the exact same coordinates as its predecessor adds nothing a neighboring identical point didn't already carry. The other three are reported, not corrected: there's no safe way to guess what a backward timestamp should have actually been, whether a multi-minute gap represents a real pause or something else, or what the "correct" position was for a fix that implied an impossible speed. Those are judgment calls the data itself can't resolve, so the tool tells you exactly where they are instead of guessing.
Where each step happens
- Checking the track — the GPX Cleaner is the tool this guide is built around, and the one place to remove exact duplicates automatically.
- Looking at the result — the GeoJSON / KML / GPX / CSV Viewer renders the track on a map, useful for visually confirming a flagged section (a long gap, an implausible jump) against the actual route.