Ask Rick: do iPhone and iPad use GPS?

Could you please tell me if the iPhone and iPad is using a GPS aerial to establish its location? Or is it using a triangular system of telephone masts? If it is GPS, I would like to use it as an emergency backup for the navigation equipment on my boat, even in the middle of the North Sea. Henrik Bessermann, by email

All iPhones from the 3G model onwards and 3G iPads have what is known as assisted GPS or A-GPS and this works in several ways. Firstly it uses phone mast triangulation and Wi-Fi hotspots to obtain a quick and dirty fix on your location, normally to within a kilometre or less, depending on the area. This is then used to help speed up the acquisition of GPS satellite signals, to provide a more accurate position, this time to within a few tens of metres. The GPS function does work without a network connection but it can take a minute or more for it to lock on to the satellites and work out your position.

The network connection is also used to update map information and provide extra detail, though clearly you are not too worried about finding the nearest McDonalds or Post Office bobbing around on the North Sea. As a matter of interest iPhones and iPads send details of your location to Apple. This is used to maintain a crowd-sourced database of phone masts and Wi-Fi hotspots, which is supposed to help refine the initial location fix. Apple is keen to make it clear that this information is encrypted and anonymous, though a bug discovered in 2011, now fixed, revealed that an unencrypted file on iPhones stored a year’s worth of time-stamped location data. This data is still retained, but now only for 7 days.