Multiply the stated map length by the ground distance represented by one map unit. Use the printed numbers, not a ruler on a resized screen. These flat practice maps are invented.
Worked example
If 1 map cm represents 2 km, a 4 cm route represents 8 km.
A four-division scale bar labels 0, 2, 4, 6 and 8 km. Each nominal one-map-centimeter division represents two kilometers. The on-screen size is not guaranteed to measure four centimeters.
