**Geodetic surveying** is the survey in which the curvature of the earth is taken into account and higher degree of accuracy in **linear** and **angular** observations is achieved. The geodetic **surveys **extend over large areas and lines connecting any two points on the surface of the earth are treated as arcs. For calculating their projected distances on the plans or maps, the correction for the earth’s curvature is applied to the measured distances. The angles between the **curved lines** are treated as spherical angles. A knowledge of spherical trigonometry is necessary for making measurements for the **geodetic surveys**.

## Scope and Use of Geodetic Surveying

Geodetic surveys are conducted with highest degree of **accuracy** to provide widely spaced control points on the earth surface for subsequent **plane surveys**. Provision of such control points is based on the principle of surveying from the whole to the part and not from the part to the whole, as stated earlier. Geodetic surveys require the use of **sophisticated instruments**, accurate **methods** of observations and their computation with accurate adjustment. To eliminate the **errors** in the observations due to refraction, angular observations are generally restricted to night and arc lamps are used as signals on the survey stations.

## Division of Geodetic Surveying

Geodetic surveying can be divided in the following ways.

### Triangulation

In this type of surveying a network of well defined **triangles** are formed on the plot of land to be surveyed. Only **one line** known as **base line** and all other angles are measured very carefully.

### Reciprocal Leveling

This type of surveying is required to obtain the difference in levels between two points which are separated by obstacles.

### Stadia or Tacheometric Surveying

Is is a type of surveying in which vertical and horizontal distances are computed from stadia readings without using **chain** or **tape**.

### Astronomical Surveying

It is a **branch of surveying** in which the meridian, azimuth, latitude, time etc of a place on the surface of the earth are determined by **observation** of some bodies like the sun and the fixed stars.

### Photographic Surveying

This is a method of surveying in which plans or **maps** are prepared from **photographs** taken from suitable camera stations.

Dear sir,

I am in Tamil nadu.

I could not create a layout with FMB sketch available, I need some more details which I don’t know how to read from the chart which is available alongwith FMB.

If some one help me how to read the FMB sketch in relation with the tabulation it would be useful.