In reply to olddirtydoggy: You're dealing with the age old problem of projecting a sphere onto a flat piece of paper, or for a GPS, converting from a lat long derived from the sphere to a regular xy grid. Somewhere along the line something is going to get stretched, or you're going to get holes in the map.
Different areas use different transformationsto do this, minimising distortion as best as they can. The OS grid is a good example - works very well for the UK, not so well elsewhere. Generally NS movements and extent are bigger issues than EW - fundamentally a 1degree EW increment at the equator is a lot bigger than near the north pole , so there's a lot of stretching, and a lot of error/inaccuracy.
Czech republic to Iceland is smaller, but the same issue. I cut images from Iceland from the two maps and overlay them - ratio NS to EW is not the same.
I also noticed a thread recently where someone was asking for Alpine maps to go into the OS app. I don't know how that projects internally, and the latitude difference isn't so great, but 10m of error can start to mean something..
Post edited at 11:30