Device Distance Recording Accuracy

May 2020

 After a hike there is always some discussion about why there are so many variations in the distance recorded by phones and devices. 

I will try to explain the main reason why this occurs as simply as possible. I have included some screenshots of the track recorded by my Garmin on a recent hike which clearly show why the device continues to add distance even whilst stationary. 

GPS devices (which include phones) gather data from a group of 27 satellites that orbit Earth twice a day, following exact trajectories such that, at any given time at any given location on earth, at least four are visible. 

Those satellites send out radio wave signals picked up by your device. Based on the time difference between when the wave was sent and received, a GPS unit figures out how far away each satellite is and uses that info to pinpoint your location—a process known as trilateration. 

With the US Global Positioning System (GPS) there is a margin of error. Depending on many factors the discrepancy is up to fifteen metres,

The device records your route as a series of 'waypoints' which are a set of recorded positions, for example your device will record a waypoint every 10 seconds. The distance travelled is then calculated by 'joining the dots'. Yesterday's hike resulted in around 2,400 waypoints.

A screenshot of our morning tea location as shown on the device: 

As you can see the GPS device continued to record waypoints whilst we were sitting still!! The final distance shown on the device at the end of the hike was 16.6km. Watch what happens when I delete all the superfluous waypoints

As you can see at the bottom of the screenshot there are now 2,352 waypoints and the distance has been reduced by one kilometre precisely!

The same for our lunch stop. 

Prior to me removing the superfluous waypoints there are 2,352 recorded points and the distance travelled is 15.6km 

After deleting 59 superfluous waypoints the distance is now a total of 15.4km a total reduction of 2.2km. 

When I first obtained my Garmin GPS device, I discovered that there was a settings option for how often waypoints were recorded. There are five settings from ‘Most Often’ to Least Often’. I set mine for ‘Most Often’ in the mistaken belief that this would give me the most accurate distance after a hike. In the recording above it was set to ‘Normal’ 

I hope this explains things in a way we can understand!! 

NOTE: December 2023 update. I have now acquired a newer model Garmin which automatically stops recording waypoints after I remain stationary for more than 30 seconds resulting in a much more accurate distance.