In this method, the area to be surveyed is divided into a grid or series
of squares. The grid size may vary from 5 m x 5 m to 25 m x 25 m depending upon
the nature of the terrain, the contour interval required and the scale of the
map desired.
Also, the grids may not be of the same size throughout but may
vary depending upon the requirement and field conditions. The grid corners are
marked on the ground and spot levels of these comers are determined by
leveling.
The grid is plotted to the scale of the map and the spot levels of
the grid corners are entered. The contours of desired values are then located
by interpolation.
Special care should be taken to give the spot levels to the
salient features of the ground such as hilltops, deepest points of the depressions,
and their measurements from respective corners of the grids, for correct
depiction of the features. The method is used for large scale mapping and at
average precision.
