Surveying is the art of making Such Measurements as Will determine the relative positions of points on the surface of the earth in order that the shape and extent of any portion of earth’s surface may be ascertained and delineated on a map or plan. It is essentially a process of determining positions of points in a horizontal plane.
Levelling is the art of determining and representing the relative heights or elevations of different points on the surface of the earth. It is the process of determining position of points in a vertical plane.
Surveying and Levelling are frequently considered as distinct operations. However, in its comprehensive sense, the term surveying includes levelling.
Purpose of Surveying
The primary purpose of survey is the preparation of a plan or map. The results of surveys when plotted and drawn on paper constitute a plan. A plan is therefore the representation of to some scale, of the ground and the objects upon it is projected on a horizontal plane. The representation is called Map if the scale is small while it is called Plan if the scale is large e.g a map of Pakistan and a plan of a Building.
Primary Division of Surveying
Surveying may be divided into two general classes:
1) Geodetic Surveying
In Geodetic surveying also called Trigonometrical Surveying, it is necessary to take into account the curvature of the earth. Since shape of the earth is spheroidal, the line connecting any two points on the surface of earth is curved or is an arc of a great circle.
2) Plane Surveying
In a plane surveying the curvature of the earth doesn’t take into account, as the surveys extend over small areas. The earth’s surface is considered as a plane, the line connecting any two points as a straight line and the angle of polygons as a plane angles. It is therefore involves knowledge of geometry and plane trigonometry. American surveyors put the limit at 250 km2 for treating the survey as plane.
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