By now you’ll probably have seen news reports saying that iOS devices maintain a file containing all the places the device has been, as determined by triangulation from mobile phone base stations. The file gets synced to your PC or Mac by iTunes.
The file was discovered by Alasdair Allen of the University of Exeter while looking at ways to visualize the radiation levels in the region around Fukushima.1
Allen and Pete Warden released a handy Macintosh application iPhoneTracker for looking at the contents of the file.2
According to F-Secure, this data is sent to Apple twice daily if you agreed to allow iTunes to send ‘diagnostic’ information to Apple.
It’s fascinating to see this data. I just wish Apple had had the decency to tell us about it.
On the right you can see some of my travels as recorded in this file. Note how the triangulation occasionally goes very wrong: presumably when only a small number of base stations are in range, attenuation due to buildings, tunnels etc can leads to very wrong estimates of distance. Maybe you could post-process the data to remove these anomalies by imposing some kind of maximum speed, but the iPhoneTracker app does not attempt to do this.
To give you some idea of the accuracy of the track, here’s a comparison based on the “Double Dutch” audax I rode a couple of weeks ago. On the left, the actual journey. On the right, the points recorded by the iPhone.3
^ Though it has apparently been known about in the forensic computing community for a while.
^ Amusingly, this caused a big spike of requests for the OpenStreetMap tile data:
^ There were also a few points recorded lying outside the rectangle shown.