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Elevation for Your Activity

posted this on February 7, 2012, 1:32 PM

Strava uses a variety of methods to calculate elevation. This article goes over frequently asked questions and outlines how we calculate elevation in different scenarios. 



How Elevation is calculated

It is important to remember that elevation data from all sources (barometric altimeters, GPS signals, and databases) is subject to error and that the elevation gain for an activity is an estimate. We are always working on improving our elevation data sets and algorithms.


Elevation on a segment

Segments are always created from a Strava activity and as a result, they inherit some of that activity's characteristics.

  • If the original activity was recorded by a GPS device with a barometric altimeter, the segment will use the barometric data recorded by that device.
  • If the original activity was not recorded by a barometric device, or if a Strava admin has rebuilt the elevation for that segment, then we will cross-reference the GPS data to an elevation database in order to find the elevation. 


Elevation on an activity

Elevation on activity pages will be calculated in one of two ways: cross-referencing the GPS data to a database or by using the barometric data in the original file.

  • Device with barometric altimeter:  If the GPS device used to record your activity has a barometric altimeter, Strava will use the elevation data in the original file. We do some smoothing to the data, which includes discarding outliers to reduce noise. The amount of smoothing is less on activities with barometric data than it is for activities without barometric data. If your device has a barometric altimeter, but your elevation is being recalculated, please refer to this FAQ. 
  • Device without a barometric altimeter and the Strava mobile app: If your activity was recorded with the mobile app or with a GPS device that does not have a barometric altimeter, Strava will recalculate the elevation by comparing the GPS data to an elevation database. We do some smoothing to the data, which includes discarding outliers to reduce noise. The amount of smoothing is more on activities without barometric data than it is for activities with barometric data. The accuracy of this calculation is dependent on your GPS data as well as the accuracy and resolution of the database for that region. 


Elevation on a route

Our Strava Route Builder uses our own personal database to calculate elevation data. The GPS data of the route gets cross-referenced to this database when Route elevation is calculated. This is not the same database that we use for activity elevation. 



Why is my activity's elevation different than my friend's?

Even though you may have done the exact same ride as your friend, each GPS devices will record its own unique set of data. This GPS data will always be different because of the inherent variables involved in recording GPS data: recording interval (the time between GPS points), signal strength, GPS hardware, etc. The differences in the GPS data may cause differences in the calculated elevation data.

Another source of confusion is comparing elevation data from an activity with barometric data to that of an activity that has gone through our correction process. Both are accurate ways of totaling elevation for GPS data, but the 'corrected' data is getting cross-referenced to an elevation database whereas the barometric elevation is being pulled from the data the barometric altimeter recorded into the file.


Why is my activity's elevation different than the route I created?

Routes cross-reference our own personal database for elevation while activities will use either a national database or barometric data. For more information, see this section of our elevation article. 


My device has a barometric altimeter, why is Strava recalculating the elevation?

If you recorded your activity with a GPS device that has a barometric altimeter, but Strava isn't using that data, it's possible that device is not yet in our database or that the file you uploaded is missing a Device ID. We occasionally see this when activities get synced through 3rd parties so if you know the device is in our database, please try uploading the original file from the device. If you still have questions, please submit a support ticket and include a link to the Strava activity. 


How do you calculate elevation gain?

Elevation data on Strava is smoothed to take out noise— we have a 'threshold' where climbing needs to occur consistently for more than 10 meters before it is added to the total elevation gain. If we did not have this threshold, the elevation numbers would be inflated for longer activities. This gain threshold applies for both rides and runs. 


My friend and I are using the same GPS device, but our elevation is different for the same ride—why? 

Please refer to this section of our elevation article.


Why does Strava recalculate my elevation data? My device records its own data. 

Because elevation data derived from a GPS signal is fairly inaccurate, Strava automatically corrects elevation derived from a GPS source by consulting elevation databases to determine the elevation at each point in the activity. Our thresholds and smoothing process may differ from that of the other platform or GPS device. 


The data recorded by my barometric altimeter is wrong, can I correct this?

If you suspect that your elevation data is incorrect, you can request an elevation lookup.  Click on the "Elevation?" text under the elevation statistic in the overview (shown below). A dialogue pops up with a button to "Correct Elevation." This button will only appear for data collected with a barometric altimeter (or in rare cases where a previous automatic elevation correction failed.) After a short while, the "Calculating" text will change to "Updated," and if you click on "Updated" your page will refresh with the new elevation data. While it is possible to revert back to the barometric data, this will require your activity to be reuploaded and you will lose any kudos/comments on that activity. 

Elevation Correction


Can I edit the elevation on my activity?

No, it's not currently possible to make a manual edit to the elevation on an activity. 


Can I input elevation for manual activities?

Not at this point in time, but you can vote for that feature here.


Why is the elevation total on the segment page different than on my activity?

The elevation stat reported on the segment leaderboard page may differ from the elevation stat you see next to your segment effort on your activity. This is because the elevation stat on your segment effort is based off of the data in your file. Please refer to this section for how each stat is calculated.

Segment elevation as shown on Segment Leaderboard Page Elevation for a segment effort on an activity 
Strava_Segment___Sausalito_to_GGB.png Drizzly___Ride___Strava.png




The Details 

Elevation databases

For devices without barometric altimeters, we consult elevation databases to determine the elevation at each point in the activity. The resolution of these databases can vary based on location. For example, the USGS National Elevation Dataset (NED), which we consult for activities located in the US, generally has a 10 meter resolution though some small areas have a 3 meter resolution. For activities located outside of the US, we consult the ASTER and SRTM databases which have a resolution of anywhere from 30 to 90 meters. 


Barometric altimeters

Barometric altimeters determine altitude by measuring atmospheric pressure. Measurements can be affected by changes in the weather or the sensor holes getting blocked by water or other debris. Device manufacturers may provide basic calibration procedures. For example, Garmin devices with barometric altimeters allow a certain number of manual elevation points to be set; starting an activity near an elevation point causes the device to use the known elevation as the starting point. Consult the manual for your device to learn about calibration procedures. We generally consider the data from barometric altimeters to be of higher quality than the data derived from GPS signals and prefer that when processing activities.


Typical problems with barometric devices:

The elevation profile looks like it is drifting over time. This can happen with barometric altimeters as the weather changes (eg. the atmospheric pressure rises or drops, causing the altimeter to measure as though it is at a lower or higher altitude).


Other Known Issues and Problematic Terrain:

  • The activity has areas where the elevation is zero or is very linear. This can happen when crossing bridges or through areas that don’t we don’t have coverage for. Coast lines can be particularly problematic. We attempt to fill in the data by interpolating data; the interpolation depends on where the missing data begins and ends.
  • The elevation profile has climbs, but the elevation gain is very small. We smooth the data before calculating gain and depending on the resulting data, elevation changes may not be enough to pass a threshold that we use for determining whether or not you have gained elevation.
  • The elevation profile has climbs, but the elevation gain is very large. This often happens with activities recorded in mountainous areas outside of the US. The resolution of the data sets can be coarse and the profile may be bumpier than it should be even with interpolation and smoothing. Sometimes they are so coarse it's like trying to find a smooth elevation profile over a lego block model of your area. These bumps may pass the threshold in gain calculations and the total gain from the bumps may add up to more than the gain that was perceived on the ride.
  • Differences can also occur between elevation databases, as the database for U.S. elevation data is different in resolution from the international elevation database. With different databases, it is difficult to control all the variables to produce the most comparable results.


Elevation Challenges:

Strava hosts a variety of athletic challenges for our athletes, some of which have elevation/climbing goals. Due to the high visibility of these challenge leaderboards, elevation based errors will surface more easily than they would normally. As mentioned above, there are many uncontrollable variables involved in calculating elevation gain. These variables can lead to exaggerated elevation totals, particularly if the activity takes place in an international, mountainous or coastal region. If you notice activities with inaccurate elevation gain, please do not flag them. Most of the time this is a result of poor database resolution, which is out of the athlete's control. If you have a question about a specific activity, or feel you've found an activity that is far too distorted, please submit a support ticket so we can take a look. 

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