iPhone 6s health app underestimates distance

health app systematically underestimates the distance we have walked.

I have seen that I am 1,5-2km behind every 10km we walk, i.e. I am loosing 15%-20%

The Health up accuracy should improve over time. Each person's steps are different size.

health app estimates the distance my taking gps location data at specific time span

The primary data comes from counting steps. GPS data is also used, but mainly to calibrate your individual step size and in case step counting doesn't work for some reason.

Any help please on how to overcome this issue?

Experiment with where you hold the iPhone while walking and be consistent about it. Some locations, like in a bag, might not work at all for step counting. I find that simply keeping it is sweatpants pocket works very well.

So, you claim that if you walk (or run) on a stationary treadmill, in circles that are too small for GPS resolution, or indoors where there is no GPS, the iPhone won't know that you're walking (or running)?

Whatever makes you happy...

1. No, there is no GPS signal in my high-rise building, nor my office building. GPS requires line-of-sight.

2. Yes, public GPS uses the same satellites as 10 years ago (actually, they're much older than that). The incremental improvements in accuracy are due to supplementing GPS data with cell tower triangulation and known Wi-Fi locations.

3. No comment.

You added very important information in your second post that is helpful in understanding what's going on. But with your attitude, I'm gone from this discussion.

Good luck.