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Garmin Connect - Course Innacuracies vs GPS measured distance

Hello,

Forgive me if this has been covered before, I have tried to do a search but might not be searching for the right words in the forums.

A couple of weeks ago, I ran a 20 mile run, and recorded it on my Forerunner 620. Link to the activity below:
https://connect.garmin.com/modern/activity/1049205237

I then mapped out the course using the Courses feature on Garmin Connect for comparison after the run. Link to Course for comprison below:
https://connect.garmin.com/modern/course/11729162

Comparing the two, the route plotted in Courses on Garmin Connect came out at 21.59 miles! That's a 7.95% inaccuracy over the measured distance using GPS.

Now, I tried hard to be as accurate as possible mapping out the route on Garmin Courses, and I admit during the 20 mile run I did take a few short walking breaks, but no way was I walking for 1.59 miles!

I have been caught out with this before, plotting out routes of various distances on Garmin Maps and then being frustrated when I come up a mile short even though I have stuck closely to the planned route.

My question is, is this an accuracy issue with Garmin Maps in the Courses feature of Garmin Connect, or is this an accuracy issue with the Forerunner 620 nnot recording the route acccurately?

Thanks

0 JSRUNNER_ over 8 years ago

If you look at the track recorded by the watch you will see that it has not recorded accurately. It cuts corners runs down the middle of the River Lea for a long time - goes straight through a large building near Angel. This could be down to several things - I have found that you need to make sure that yu give enough time before starting a run to get a good GPS satellite acquisition. I include GPS accuracy as a field on my run screens on my 920 and make sure it says good before I start a run. Are you using smart recording? Does the 620 have Glonass - if so is it on or off? My first 920 gave inaccuracies - and I ended up getting the device replaced and touchwood the new one is OK. If you are regularly getting these types of inaccuracies then I think that is too big an error and I would return the watch. Amazon replaced mine with no issues. I have to say that generally accuracy of track was/is better on my 610 than on the 920 this is counterbalanced by the additional features that it gives me but disappointing nevertheless.