Google has launched a new version of its popular mobile maps application. The most interesting feature is its ability to show your position without the need for a GPS unit. It does this by triangulating your position from the available mobile phone cells you are in. This is then presented as a flashing blue dot and a larger shaded circle to show the margin of error.
In use pressing 0 moves the map and blue dot to your current position and a message at the bottom tells you the margin of error. So far this has ranged from 500 to 1700 metres. In practice the margin of error is greater than this as not once yet has my actual position been in the blue shaded area but close to. I guess that the accuracy must depend on the number of cells that can be found.
So not a tool to give you accurate driving directions but something to confirm the general area you are in. Or as my friend David puts it to confirm that you are not in Swindon when you are actually in Reading.