A question arose about the scale and distances involved on a particular map we were reading, something like, "How big is this map?" There was no Distance Scale Rule printed on the map, save the chilly numbers 1:250,000. Ok that's 1 bit on the map = 250,000 bits on the ground right? So how far is it between here and there...

In this digital age it is easy to print a map at and make it larger, perhaps to make it easier to read. However the map was originally drawn at a particular scale, for example 1:250,000 which equated to 1" representing 1 mile.

The distance between two towns on the map is now longer, but the scale is still 1:250,000. The map has become distorted and will no longer be accurate when used to measure distance.

The relative positions of details on the map remains the same, but their distance apart can no longer be measured accurately.

If the cartographer who wrote the map included a 'linear scale ruler' and the map had been reproduced at at different physical size, then the drawing of the 'linear scale ruler' will stretch and become longer or shrink and become shorter in the same proportion as the features on the map.

Only maps displaying the linear scale ruler can be reproduced at different sizes and remain useful for measuring distance. For this reason alone map-makers tend to include a linear scale ruler, as the only method of showing a map's scale.

The table below shows the scale in Imperial measurements.