Calculating Distances on Maps

It is often desirable to use a map to calculate a distance on the ground. If you understand scale ratios, it is very easy to do the calculation

Example 1 The distance to be travelled measures 5.5 centimeters on a 1:10 000 map.  What distance is this on the ground?  Calculation:  1 centimeters represents 10 000 centimeters  so 5.5 centimeters represent 5.5 x 10 000 centimeters  = 55 000 centimeters  = 55 000/100 meters  = 550 meters  Example 2 The reverse calculation is also sometimes useful. For example if a toxic spill will affect all residents within 1km of the spill site, how many streets of houses will have to be cleared? Pollution may travel 1.5km from a spill site, what sized area will be affected on a 1:10 000 map?  Calculation:  1.5km = 1.5 x 1 000 meters  = 1 500m  = 1 500 x 100 centimeters  = 150 000 centimeters  10 000 centimeters is represented by 1 centimeters  so 150 000 centimeters is represented by  150 000 / 10 000 centimeters  = 15 centimeters  The area affected will be given by a circle with radius 15 centimeters.