HKQuantityTypeIdentifierDistanceSwimming — reading swim distance from Apple Health
HKQuantityTypeIdentifierDistanceSwimming is measured in metres and, in a pool, has never seen a satellite — which changes what “wrong distance” means.
Open your file
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export.zip straight from the Health app — do not unzip it
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Strokes and turns, not GPS
Underwater, GPS does not work. In a pool the Watch counts lengths from wrist motion and your set pool length; in open water it uses GPS between sighting strokes. So a pool distance that is off is usually a wrong pool-length setting or a missed turn, not satellite error — a different diagnosis from a cycling route that wandered. The identifier is stored in metres regardless, where walking and cycling distance default to kilometres.
Open water is a different measurement again
In a lake or the sea, the Watch cannot count lengths — there are none — so it falls back to GPS sampled between strokes, when your wrist breaks the surface. That makes open-water distance noisier than pool distance and prone to overshoot: every sighting stroke that snags a satellite fix adds a little zig-zag the straight-line swim never made. The same identifier holds both, so a history that mixes pool and open-water swims mixes two quite different error profiles under one number.
What you get from this page
This page reads your swim-distance records in metres, with their timestamps, on your device, and keeps pool and open-water swims legible rather than averaging away the difference between how each was measured. It answers “is this the distance I actually swam” by showing you what the file holds, not by re-deriving it.
This identifier is one of dozens. The Apple Health data dictionary lists every identifier this parser reads, with its canonical type and unit.