A lot of iPhone 3G/3GS customers are complaining of GPS accuracy problems.
One thing I try to tell everyone is that the iPhone GPS quality isn’t anywhere near as good as regular GPS Receivers. Although a lot of people don’t want to believe this until they start seeing problems, they eventually come down to earth with a massive thump.
I have carried out a lot of accuracy tests with the iPhone and the problem is massively down to attenuation and accuracy of your current position.
A great way to test this is with other applications, if you think you are experiencing problems, pull over and stop the car. Run up another app like Digital Compass – @ 59p. This provides you with a great feature called GPS accuracy where you can check how accurate your GPS fix really is.
Remember that GPS horizontal accuracy should be around 15 meters off and vertical accuracy can be up to 50 meters off. One thing to mention is that the iPhone’s GPS accuracy (or inaccuracy) isn’t always a problem. Some days or trips you get perfect uninterrupted coverage, other times it can be a good 50-100 meters off . Please don’t treat this as a “don’t get a SatNav for the iPhone” as SatNav works very well on the iPhone, especially CoPilot Live 8 for iPhone, it’s just don’t expect it to be a perfect experience compared with PND’s / AIO’s (All In One’s) or other SmartPhone/Pocket PC’s.