Dividing the areas by 10, you get 1 square inch corresponding to 2500 square miles. Those areas are equivalent to 1 inch square and 50 miles square. Hence the scale factor is 1 inch : 50 miles.
Sometimes map scales are expressed as a dimensionless ratio. The number of inches in 50 miles is
... (50 mi)×(5280 ft/mi)×(12 in/ft) = 3,168,000 in
so, the map scale can be expressed as 1 : 3,168,000.
