Table of Contents
Aim:
To plot the contours of an area by method of squares (or gridding).
Equipment and Accessories:
Automatic Level, tripod, Levelling staff, chain, tape, cross staff, arrows, ranging rods, pegs, hammer, Levelling book, pencil and eraser.
Principle:
The method of squares is also called coordinated method or gridding of locating contours. The entire area is divided into squares or rectangles forming a grid. The reduced levels of the corners are then determined by differential Levelling. The reduced levels are then plotted on the plan showing the same grid drawn to a suitable scale. After choosing suitable elevation values for contours to be drawn, the required contours are plotted by means of interpolation.
Procedure:
- On the parcel of the ground for which contour map has to be made establish a square grid of points at a suitable interval ( anywhere between 3m to 20m) by means of direct ranging and fix arrows as shown in figure given below.
- Carry out differential Levelling to find the R.L.’s of every arrow point and enter the readings in table.
- Draw the same grid that is established on the ground on the drawing sheet to a suitable scale.
- Indicate on the drawn grid the reduced levels of each grid point.
- Choose suitable values for elevations of contour lines.
- Draw contour lines on the grid by interpolation.
Fig.27 Contouring
Observations & Calculations:
TABLE :
| S. No. | Grid point | B.S.
(m) |
I.S.
(m) |
F.S.
(m) |
H.I.
(m) |
R.L.
(m) |
Remarks |
Result:
Contours of the given area are plotted.
