Since the surveyed area is very large, it is never possible to make full size drawing. For convenience it is generally necessary to draw them to a reduced size, this operation is called “drawing to scale”.
There are two types of scales used in surveying.
1. Numerical scale.
2. Graphical scale.
A. Numerical Scale:
Numerical scale is also further classified into two general types.
1. Engineer’s Scale
2. Fraction Scale.
1. Engineer’s Scale:
In engineer’s scale, the scale of a map or drawing is the proportion which every distance on the map or drawing bears to the corresponding distance on the ground.
Example: 1 cm = 10 m
This means, 1 cm on the drawing represents 10 m on the ground, the scale of the map is 10 m to 1 cm.
2. Fraction Scale:
The scale is also expressed by means of a vulgar fraction whose numerator is invariable unity. The fraction is called “Representative Fraction” or RF. It is, therefore, the ratio of map distance to the corresponding ground distance. In forming the representative fraction both numerator and denominator must be reduced to the same denomination.
For example, if the scale is 10 m to 1 cm, the RF of the scale is 1cm/10x100cm = 1/1000
B. Graphical Scale:
On a graphical scale, the units of measurement should always be stated.
Characteristics Of a Good Scale are:
1. It should read to the greatest accuracy required.