A tap on the window

It was a childhood dream of mine to have large-scale Ordnance Survey maps on a mobile apparatus that I could have on my lap in a car. Back in the late 1950s I thought only of a paper map in a long strip, that rolled north and south. I couldn't see how it could be made to roll east and west also. I made do with real maps, bought in shops, that covered fixed areas. I never had a problem with