Julia J. Quinlan 
Scale and Distance in Maps [PDF ebook] 

Without a scale, the people reading a map could only hazard a guess as to whether the distance between two points on it is a matter of a few hundred feet or a few hundred miles. This useful book teaches kids how to use a map scale to determine distance, both as the crow flies and based on a particular route. It also discusses working with map grids and using a map to plan a trip.