Introduction

If you have heard about or if you have worked with a construction project or if you have ever planned a travelling trip using the google map then you might wonder that how those construction drawings and those maps are prepared.  Those maps are prepared to help you and they can help you only if they are prepared accurately.

surveying is considered to be an art of determination of relative position of a point on, below or above the surface of the earth. To fix the position of a point we have to take some reference point, for example to locate any point on the earth we have to find out its longitude and latitude.

Every point on the earth has unique co-ordinate i.e longitude and longitude.  The place on the earth where these co-ordinates originate is the Green-witch in London.

Aim of Surveying

Now the main aim of any surveying project is to prepare a plan or map of a place.  When the drawing is of a relatively small area then it is known as plan but if it is of a large area then it is known as a map. For preparing a plan we use the chain surveying, compass surveying, plane tabling or some other methods of surveying which do not take the error due to curvature of the earth into consideration.

To prepare a map of a country we have to consider the error due to curvature of the earth, because we have locate the boundaries correctly. We have to carry out the astronomical surveys. In maps we locate the vertical position of a point using the contours so we have to carry out the levelling to plot the contours. Levelling is another branch of surveying which is used to determine the elevation of a given point or to locate the points at some given elevations.

For example to the Mount Everest is at an elevation of 8, 848m from the mean sea level, that is the vertical distance of the top of the mountain from the top mean surface of the water level in the sea.

Primarily we divide the surveying into to categories namely :

1. Plane Surveying
2. Geodetic Surveying

As we know that the shape of the earth is ellipsoid. So what ever linear measurements we take along the surface of the earth they are are not straight lines but are curved lines.

In plane surveying we neglect the curvature of the earth so we consider the earth to be a plane surface. The results we get are not totally accurate but have some error with them.

In Geodetic surveying we do the survey to get the most accurate results. You have to consider the curved surface of the earth, i.e. you have to remove the error due to curvature.

Plane surveying is carried out to prepare plans and geodetic surveying is carried out to prepare the map. Geodetic Surveying gives more accurate results so it can be used to locate the boundaries of a country.  We can use the satellite images also to get the idea of the map of a country.