Gavin, thanks for your comment. Unfortunately this is a difficult one cos we want to show the satellite imagery rather than the map detail because the imagery is correct whereas the google map detail may often be incorrect - the map projections means that the maps are always slightly different to what is on the ground - I think this has to do with representing a 3-d surface in 2-d, and also google (which is the norm) treat the earth as an spheroid, where in fact it is an oblate spheroid.