In theory, GPS fix quality is roughly the same in all mid-latitudes[0]; any difference between Florida and Washington should be lost in other factors. Probably

In theory, GPS fix quality is roughly the same in all mid-latitudes[0]; any difference between Florida and Washington should be lost in other factors. Probably, either your sky is more covered in Seattle (by trees and hills, for example), or there’s more reflection and interference in the radio signal. 0. http://blogs.agi.com/navigationAccuracy/?cat=4 http://blogs.agi.com/navigationAccuracy/?cat=4 has some nice illustrations. “DOP” is a sort of ideal fix quality, with smaller numbers meaning more accurate fixes (under various assumptions); Wikipedia will explain the math. Edit: https://gps.afspc.af.mil/gpsoc/PerformanceReports.aspx https://gps.afspc.af.mil/gpsoc/PerformanceReports.aspx is a live-ish map. When I check it, FL and WA are both in the lowest (best) category. However, it’s worst-case DOP for only the 4 best satellites; under a clear sky, a good receiver will usually see several more. I often get DOPs of 1.5 in residential neighborhoods.