Surveying – Primary Division

Introduction

Before discussing the classes of Surveying, namely, Plane and Geodetic Surveying, few relevant definitions are to be understood. Surveying is an art of determination of the relative position of the points on above or below the surface of the earth by some direct or indirect linear and angular measurements.
Levelling is a branch of surveying in which we locate the points at some given elevation or determine the elevation of the given points.

The main objective of the surveying is to prepare the maps or plan of a given area. The term map is used when we have to prepare the horizontal projection of a relatively larger area on a paper sheet. The term plan is used when the area is relatively smaller.

Primary Division of Surveying

Earth is an ellipsoid. There is a difference of about 43km between the diameter of the earth along the equatorial plane and that along the polar axis. When we draw a triangular traverse on a level surface  then the triangle formed is known as a spherical triangle and the angles are known as the spherical angles.
When we draw the chord of a 12km level arc the difference in the length of the arc and the corresponding chord is only about 1cm.
Now according to the magnitude of the area and the required precision, we can classify the surveying in two classes.
(1) Plane Surveying   (2) Geodetic Surveying

(1) Plane surveying

In the Plane Surveying, the earth surface is considered as a plane surface. The error due to the curvature is neglected.
The level lines are straight lines and all the plumb lines are parallel to each other.
It is used for relatively small areas of a magnitude of near about 256km2.

(2) Geodetic Surveying

In geodetic surveying the curvature of the earth is taken into consideration, so all the level lines are taken as the curved lines.
To get precise results it becomes necessary to adopt the geodetic surveying in the areas larger than the magnitude of about 260km2.
It is more precise than plane surveying. The maps are prepared using the geodetic surveying.
It is also known as the trigonometric surveying.