I've used an OSX App to take a look at the data on an iPad I'm evaluating.
I live in Felixstowe and commute to Huntingdon, with the odd bit of work in Peterborough and Cambridge.
This is the data collected around my commute:
Note the odd one near Norwich and the ones around the North East of London? Well, I haven't been there since I've had this device. Notice also that the points seems to cluster around larger towns - I've used Waze on this iPad while driving so I was a bit surprised that the dots didn't follow the route that I use, the A14.
Here's a zoomed in part around where I live. The dots appear to be in a regular grid with only one small dot on my house:
It seems that the iPad\iPhone is only storing an approximation of your devices location.
The App I used can be obtained here:
They also have a nice FAQ:
Links to news stories here: