What is Scale?
Most maps are made to a certain scale.  The scale is normally stated on the map in numerical terms and with a bar scale to assist visually. It helps in understanding the ratio between what is viewed on the map and the what the actual distance is in reality.  A measurement of a distance on a map can be taken and the distance in the real world can then be calculated.
 
 
Examples
In Imperial measurement, 1" on a map would equal a distance in reality - (usually stated in miles). If a map had a scale of 1" = 18 miles, a measurement on the map of 7.75 inches would indicate that the real distance to travel would be 7.75 X 18 or 139.5 miles.
In metric measurement - the same principal applies but it is expressed differently.  For example - looking at 2 centimetres on a map;
scale1
represents 1 kilometre on the ground.
scale2
The scale in this example would be 2 cm = 1 kilometre, or...
    Distance on the Map    =  2cm    =         2 cm        =      1     =  1/50,000 Scale
Distance on the Ground       1 km          100, 000 cm      50,000
 
 
 
Many maps carry a bar scale..
barscale
Graphic scales provide a direct measure of the distance over the ground represented by the corresponding distance on the map. Graphic scales are simple to use and can make estimating distances a very straightforward task.