Most of us get around cities using simple guide books and maps, but nowadays there's a much more sophisticated way of doing things. Global Positioning Systems - using satellites - can tell you to within a few yards exactly where you are, where you're going and the best way to get there. And nowadays they're not too bad a price. The Garmin Emap costs from around $250 - it's about twice the size of a mobile phone, with a small black and grey screen and all sorts of sophisticated technology inside. But are these devices any good? We posted one to our reporter Martin Stott and challenged him to put it to the test.