Does GPS accuracy get worse the longer you're out on a hike?

The short answer

Duration is not one of the inputs GPS accuracy is built from. A position fix is only ever as good as the satellite geometry and sky visibility available at the instant it was taken — how many satellites the receiver can see, how spread out they are across the sky, and how much of that sky is blocked by trees, rock, or buildings right where the phone happens to be standing. None of that resets, accumulates, or wears down over the course of a recording. A point logged at the six-hour mark of a long day is worked out the exact same way as a point logged one minute in.

What actually decides accuracy at any given moment

Every GPS fix is a small piece of trigonometry: the receiver measures its distance from several satellites at once and works backward to a position. Two things make that math more or less reliable. The first is geometry — satellites spread widely across the sky give the calculation more to work with than a tight cluster does, in the same way a wide-based tripod is steadier than one with its legs close together. The second is obstruction — anything between the phone and open sky, whether it is a canopy of leaves, a canyon wall, or a row of buildings, blocks some satellites outright and can bounce their signals off a nearby surface before they reach the receiver. Both of these are properties of where a phone is standing and what the sky looks like from there, checked fresh at every single point. Neither one is a property of the clock running since the hike started.

Why a long hike can still look rougher than a short one

A six-hour day crosses far more ground than a thirty-minute loop, and more ground almost always means more variety in what the sky looks like along the way. A morning that starts in an open parking lot, climbs through a stand of trees, drops into a narrow valley, and finishes back in the open will pass through several different accuracy conditions over the course of the day — and the roughest-looking stretch of the track is very likely to land wherever the sky was most blocked, which has nothing to do with which hour of the hike it happened to be.

There is also a simple matter of sample size. A longer hike logs more points, full stop, and a receiver logging more points has more individual chances for any one of them to land slightly off — not because its accuracy declined, but because a bigger pile of anything has more room for a handful of outliers. A twenty-minute walk with the same per-point behaviour would show proportionally the same number of odd points; there just are not many minutes for them to show up in.

The one thing that genuinely does shift over time — and it is not this

There is a real, if minor, sense in which GPS geometry changes with time: satellites orbit the earth on a schedule of their own, so which ones sit overhead, and how they are spread across the sky, is not identical at nine in the morning and one in the afternoon even standing on the exact same spot. That is a genuine property of the satellite system, not a myth. But it is a difference tied to the time of day and the date, the same for a phone that has been recording for ten seconds as for one that has been recording for ten hours — it has nothing to do with how long any individual hike has been running. There is no clock inside a GPS receiver counting up the minutes of a single walk and quietly loosening its grip as it goes.

Things that trip people up

• Blaming a rough patch late in a long hike on the GPS "getting tired" — check what the trail actually looked like at that point instead; a canyon, a dense stand of trees, or a stretch under an overpass explains it far better than elapsed time does.
• Assuming a short walk is automatically cleaner than a long one — the physics behind any single point are identical regardless of how many other points came before it that day.
• Expecting a track to keep getting smoother the longer a hike goes on, the way it settles in during the first minute or two — that early settling is a one-time thing near the start, not an ongoing improvement that continues for hours.
• Noticing more odd-looking points on a long day and reading that as declining performance — a longer hike simply logs more points, and more points means more individual chances for one of them to look a little off, at the same underlying rate the whole way through.

Where TrailCam fits in

TrailCam records position in the background for as long as a route is running, from a short loop to a full day out, without changing how it reads the sky or how often it logs a point as the hours pass. A long track and a short one are handled by exactly the same recording, just for a different length of time. TrailCam is free to download.