by Ian Duff
I have a rectangular map with dimensions 1 metre east-west, 75 centimetres north-south and a scale of 1 centimetre to a kilometre.
I have a smaller map covering the same geographical area that I have turned face down, rotated 90 degrees and placed on the larger map with its north-east corner on the south-west corner of the latter.
A pin that is pushed through both maps a whole number of centimetres from the larger map’s western edge goes through the same geographical point on both maps.
On the smaller map each centimetre represents a whole number of kilometres. How many?