All iPhones appear to log your location to a file called “consolidated.db.” This contains latitude-longitude coordinates along with a timestamp. The coordinates aren’t always exact, but they are pretty detailed. There can be tens of thousands of data points in this file, and it appears the collection started with iOS 4, so there’s typically around a year’s worth of information at this point. Our best guess is that the location is determined by cell-tower triangulation, and the timing of the recording is erratic, with a widely varying frequency of updates that may be triggered by traveling between cells or activity on the phone itself.
This sucks, especially since consolidated.db is unencrypted. Now I understand the need for iDevice full disk and system encryption, something the Defense Advanced Research Projects Agency (DARPA) is working on for federal agencies.