Only way to get accurate real time data when running is to use a good foot pod like Stryd. GPS just isn't as accurate as people think, no matter if you use Apple Watch or Garmin.
That's right, GPS error can be on the order of 10s of meters, worse in urban environments. Google (and presumably Apple) use WPS to enhance location data, meaning a triangulation (simplification here) or location based on known WiFi router and bluetooth beacon positions. They also have a team dedicated to more complex geometric calculations of how the GPS signal may be reflected given the known positions of buildings.
But if you have a clear line of sight that's a different issue. I went cycling on a path next to a river and the GPS trace was buttery smooth.
This used to be true, but in 2000 (!)the US government enabled the full range of GPS features for civilian use, vastly improving the accuracy of GPS receivers.
GPS.gov says single band receivers should be able to get less than 2m accuracy. Dual band units, like the latest Garmin Forerunner watches, can do much, much better.
But if you have a clear line of sight that's a different issue. I went cycling on a path next to a river and the GPS trace was buttery smooth.