Have trouble with inaccurate GPS data while recording your activities? See the information below to learn more about what bad GPS data is, why it happens, and how to prevent it.
What is bad GPS data?
We use the term "bad GPS data" to describe any circumstance where your GPS device records location (or other) data that does not accurately represent your activity. Bad GPS data can result in your activities on Strava having missing or extra distance recorded; segments not matched at all or recorded inaccurately; inaccurate elevation data; inaccurate achievements such as estimated best efforts; and more.
Your device may have simply lost a connection to GPS satellites and did not record any data. Your Strava activity may be missing a map, show a straight line connecting your start and endpoints, or be automatically tagged as an indoor activity.
Your device may have recorded GPS points that deviate from your true path. See the examples discussed in this article.
Why does bad GPS data happen?
Many factors contribute to the accuracy of your GPS data - and it's important to keep in mind that no data is perfect; in fact, there is some error inherent in any GPS recording. Ignoring (for now) environmental factors, different devices have different qualities of GPS hardware and software - meaning that even if your device is working at its peak performance, there will always be a margin of error in the accuracy of its recording.
GPS works by connecting your device to a number of overhead satellites and precisely measuring the time it takes for a signal to travel between your device and the satellites. Because the speed at which the signal travels is known, the amount of time the signal is in transit allows your device to calculate the distance to each satellite. Since the positions of each satellite and the distances between them and your GPS device are known, your position can be triangulated. More information can be found here.
Because we're dealing with extremely fast signals requiring precise detection, any slight inaccuracy in signal reception or disturbance to the signal itself can translate into a significant displacement of your reported position. Consequently, environmental factors such as dense trees, steep hillsides, tall buildings, or even heavy cloud cover can affect or even interrupt the GPS signal's path between your device and the satellites.
Examples of bad GPS data
GPS Drift: Below, you'll see a classic example of GPS drift where there's an area of dense, tall trees about a third of the way up the climb. As the activity below demonstrates, the GPS track follows the road with great accuracy until it enters the tree cover, at which point it begins to deviate from the road. Although you can see that the route generally follows the shape of the road, it does so with much less precision. Bad GPS data like this could cause your activity to report less distance than you actually traveled or fail to match segments you would otherwise match.
Lost GPS Signal: Environmental factors can often cause your GPS signal to be lost and, at times, reacquired. In cases like this, the pre-and post-signal-loss points will be treated just like any other two subsequent points (although more time has elapsed between them) and will be connected with a straight line. Cases of signal loss like this can cause your activity to report less distance than you actually traveled, or to not match segments that you would have otherwise matched.
GPS Bounce: Tall buildings can often cause a GPS signal to "bounce" on its way between your GPS device and the satellites; this adds extra distance - and therefore extra time - to your device's calculation of your position. As you can see below, this often results in a "jumpy" GPS track. Bad GPS data like this can often cause your activity to report more distance than you actually traveled, since each zig and zag in your GPS track has to be accounted for by a straight line connecting them. It can, in turn, cause you to receive inaccurate achievements on your activity or miss segments that you would have otherwise matched.
GPS Jump (Teleport): A GPS jump happens when your device records a location far from your actual path. It then suddenly jumps back to a point on your true path. This is different from drift, which gradually takes your path off course rather than skipping ahead. On the map, a jump can make it look like you teleported from one spot to another. A jump can also happen if your device stops recording GPS data for a while. This creates the same teleporting effect once recording starts again. If a jump happens at the start or end of a segment, Strava may have no data for that segment boundary, and a segment match will not be possible. GPS data cannot be corrected or filled in after recording. If a jump happens at the start or end of your activity, use the crop tool to remove the affected data.
How to fix bad GPS data
While Strava does its best to optimize our data analysis by ignoring the most obviously inaccurate data, in the end we can only make the most of the data provided by the GPS device. Put another way, when a device records bad GPS data, the only option that Strava has to improve it is to ignore portions of that bad data.
Unfortunately, when, for whatever reason, a portion of your activity isn't recorded by GPS, we can't "fill in" the missing data or "correct" the bad data. However, you do have a few good options to get credit for your efforts and manage the way that activities represent GPS data:
If a segment didn't match your activity but you think it should have, you can request that the Strava support team review it and attempt to force-match it to your ride or run. We cannot adjust your time on a segment, however. Here is more information about segment-matching issues.
In some cases, you can correct the elevation data calculated for your activity. More information is in our elevation FAQs.
You can crop your activity to cut out the most affected parts if the bad GPS data occurred at the beginning or end of your ride or run. Here is some more information about the crop tool.
You can create a manual activity to account for the lost mileage, though it won't count toward Strava Challenges and won't sync with any segments. More information on how this feature works can be found here.
If you were with a friend who recorded the activity with GPS, your friend could tap the Add Friend button on their activity detail page, which creates a shareable link they can send you. This will allow you to upload a copy of the activity as your own. More information on how this feature works can be found here.
How to prevent bad GPS data
Thankfully, there is more that can be done to prevent bad GPS data from being recorded than there is to repair it. As previously mentioned, different devices have different GPS hardware qualities, so while there are some device-specific tips and tricks, there are also key practices that can help improve your GPS data quality regardless of the device you're using.
Ensure your device is mounted/carried as high and as unobstructed as possible, rather than buried deep in a pocket.
Do your best to avoid environments that will always be problematic for GPS signal, such as canyons (natural or man-made), dense tree cover, and city streets lined by tall buildings.
In many cases, it will help to give your device a minute or two while you have a clear view of the sky to acquire a signal before fully starting your ride or run.
Sometimes simply turning your device off and on again, or disabling and enabling GPS, will do the trick.
As for specific devices, the manufacturer will always have the most up-to-date and relevant information, but we have some troubleshooting suggestions for Android and iPhone.