GPS watches & Smartphone Apps can miscalculate distances. Try this experiment. Run around a track and then download the map data to your computer. Your laps will rarely overlap; worst of all, they may not even appear as ovals.
Unless, of course, you get a high end GPS unit like the ones below:
How can you improve the accuracy of your GPS App.?
There are a few key settings that help you keep tabs on your accuracy:
The most important one of these is the “time interval”. Time interval is the shortest distance between two recordings of your position. You want this value to be as low as possible.
Another important setting is the “distance interval”. If your path is filled with switchbacks or just a lot of winding roads, lowering this setting will boost accuracy. Again, make the interval as low as possible.
A third setting that helps you keep track of your accuracy, but can also turn your run into a living hell, is the “GPS accuracy” setting. When your distance from a decent satellite signal is 200 meters (default distance for most GPS apps) or less, your position will be calculated and tracked. You can decrease the radius and thereby improve accuracy, BUT MAKE SURE YOU HAVE A GOOD SIGNAL because your phone will stop recording your workouts when the signal gets too weak. If you’ve refined your radius to 10 meters, then there will be MORE spots where the signal is weak, which means your phone will STOP tracking your distance. You might want to try a moderately smaller setting, such as 180 meters; although you can shrink the radius to 10 meters, it’s unlikely that you’ll be in range, especially if you live up in the mountains, like me.
A GPS App with Tweakable Settings:
My Track (Google)