Surveying - An Introduction

Surveying :- Surveying is the that branch of science which deals with the art of determining the relative positions of points on , above or beneath the surface of the earth by means of an direct measurement or indirect measurement of direction , distance and elevation. It also includes the art of establishing points by predetermined angular and linear measurements. The application of surveying requires skill as well as the knowledge of the  mathematics , physics and to some extent , astronomy.

Levelling :- Levelling is a branch of surveying which deals with the object of which is -
1. to find the elevations of points with respect to a given or assumed datum , and
2. to establish points at a given elevation or at different elevations with respect to a given or assumed datum. The first operation is requires to enable the works to be designed while the second operation is required in the setting out of the all kinds of engineering works. Levelling deals with measurements in a vertical plane.
The knowledge of surveying is advantageous in many phases of engineering. The earliest surveys were made in connection with land surveying. Practically , every engineering project such as water supply and irrigation schemes , railroads and transmission lines , mines , bridge and building etc. requires surveys. Before plans and estimates are prepared , boundaries should be determined and the topography of the site should be ascertained. After the plans are made , the structures must be staked out on the ground. As the work progresses , lines and grades must be given.
In surveying , all measurements of lengths are horizontal , or else are subsequently reduced to horizontal distances. The object of a survey is to prepare plan or map so That it may represent the area on a horizontal plane. A plan or map is the horizontal projection of an area and shows only horizontal distances of the points. Vertical distances between the points are , however , shown by contour lines , hachures or some other methods. Vertical distances are usually represented by means of vertical sections drawn separately.