The fundamental objective of land surveying is to prepare a plan or map of an area. The map thus prepared serves as the primary source of information about the surface of the earth for further engineering works.The data required for making of a map gets collected through field surveying. To start field surveying, it is required to know very accurately, the geographical coordinates (latitude, longitude) of at least one point, known as control point and the length as well as azimuth of a line, known as baseline (Figure 3.1). The Latitude of the point and the azimuth of the line are determined through astronomical survey and longitude from time measurement. The length of the line is measured with a distance measuring instrument.

From the control point in association with the base line, a number of intervisible points are selected such that on joining these points well shaped triangles are required to be formed. These triangles carry forward points whose geographical positions are calculated from the measurements (horizontal distance, horizontal angles) taken from the network of triangles. The calculated parameters undergo further adjustment by satifying the geometrical conditions associated with the parameters as well as with figures. This helps in minimisation of errors which may creep in further surveying operation. Inside the big triangles formed by widely spaced control points, network of smaller triangles get established (Figure 3.2). This process gets repeated materialising the basic priciple of surveying "to work from whole to part". Thus the entire area to be surveyed gets covered with network of triangles.

The detail surveying is then carried out within the smallest triangle. During surveying, measurements (distance, direction, angles, height etc.) for important objects/ points are taken. The measurements are then used for necessary calculations and adjustments resulting in identification and finding positions (with respect to standard reference) of salient objects.

To prepare map, first a grid of medians and parallels of latitudes is being prepared to provide a frame work of map. Control points are then plotted by their spherical coordinates.

Then objects are graphically represented in a rectangular coordinate system for depicting planimetric position. Terrain height is depicted by using contours at regular interval. The identification of objects are depicted using conventional symbols and colours Figure 2.1.

To prepare map of the area, inside the marked area in Figure 3.3, first the surveying measurements and plotting are being carried out for plot number 1(Figure3.4).

Next, detail surveying (Figure3.5) and plotting are being carried out for plot number 2 (Figure 3.6) and subsequently detail mapping is carried out for plot number 3 and plot number 4. Then, a final map of the whole area is being prepared by mosaicing the component maps (Figure 3.7)

<< Back | Next >>