Drawings are not usually made full sized, for convenience it is generally necessary to draw them to a reduced level, this operation is known as drawing to a scale.
Scale is a fixed ratio that every distance on the plan bear with corresponding distance on the ground. Scale is represented by the following method.
- One cm (1 cm) on the map represents some whole number of meters on the ground, such as 1cm = 10meters
- Representative Fraction is ratio of map distance to the corresponding ground distance in forming representative factor both numerator and denominator must reduce to the same denomination.
For Example: 1cm = 50 meters
Representative Factor (R.F) = 1/50X100 =1/5000
This shows 1cm on the map is equal to 5000mm (5 meter) on the ground.
The scale may be stated on the map graphically or by numerical relation, it should be shown near the title of the map so that it is easily visible. On graphical scale the units of measurements should always be stated.
The characteristics of good scale is, it should read the greatest accuracy required and it should be convenient to use.
Various Types of Scales
- Plain Scale
- Diagonal Scale
- Vernier Scale
- Scale of Chords
Plain Scale : A plain scale is one on which it is possible to measure two dimensions only such as units and lengths, meters and decimeters, miles and furlongs etc.
Diagonal Scale: On a diagonal scale it is possible to measure three dimensions such as meters, decimeter and centimeter and yard, feet, inches.
Vernier Scale: Is a device for measuring the fractional part of one of the smallest divisions of a graduated scale. It usually consists of a small auxiliary scale which slides alongside the main scale, it was invented by Pierre Vernier in the year 1631.
Abhijeet Baikerikar
Founder, All About Civil Engineering
