This picture shows the railroads in Texas in 1900. If a passenger wanted to travel from Bonham to Marshall, he would have to go to T.C. Park Post Office and then to Marshall. On the map, the distance from Bonham to T. C. Park Post office is 11.5 cm and the distance from T. C. Park Post Office to Marshall is 6 cm. On the the map 1cm = 13 km. Although we could measure the displacement if we had a map to scale, why can we not calculate it