What is Scale for Map? How can the Map Scales be expressed?
Maps are usually drawn to scale in order to be accurate. A scale is the ratio of distance between any two points on the map, corresponding to the actual distance on the ground. It shows how much of the actual earth’s surface is represented by a given measurement on the page of a map.
Map scales may be expressed by one of the following three methods –
By Words and Figures: By this method the scale is expressed in words stating how many units on the map equals how much on the ground. Thus 1cm = 4km means 1cm on the map corresponds to 4km on actual ground surface. This is particularly important for road maps where a person travelling from point A to B which are say 3cm apart on the map would have to travel a distance of 12 km.
Graphical or Linear Scale: This scale is shown by means of a straight line which is divided and sub-divided so that distances can be directly measured and read from the map. Each unit represents a certain number of miles or kilometers on the earth’s surface.
Numerical or Representative Fraction: This is the most common method of expressing scale giving the proportion between the distance on the map and the corresponding distance on the earth’s surface by means of fraction.
Representative Fraction = Distance on the map / Distance on the ground
It may be written as 1 : 57,000 or 1/57,000.
Thus it means one unit on the map represents 57,000 of the same units on the ground. This method is independent of any particular unit of measurement and thus can be converted to any unit thereby having a universal application. For example for an American this map scale may mean 1inch on the map is equal to 57,000 units while for an Indian 1cm of the same map is equal to 57,000 cm actually.