1" (map distance) / 63,360" (1 mile—ground distance)
if 3" = 1 mile the R.F. is:
3" (map distance) / 63,360" (1 mile—ground distance) or 1 / 21120
if 6" = 1 mile:
6" / 63360" or 1 / 10560
if 12" = 1 mile:
12" / 63360" or 1 / 5280
In reading a map one must know the scale and also where the North is. This is always indicated by an arrow pointing either to the magnetic North or the true North. If to the magnetic North the needle will have but one barb away from the true North. The angle between the magnetic and the true North is the declination.
Placing the map in proper relation to the ground so that points of the compass coincide on map and ground is called orienting the map.
In map work there is one vital point to remember; practically all the ground surface is in its present form as a result of water action