1. MEASURING THE AREA

2. Measuring the Area - Considerations
All eastings are 2 cm (1 km) apart
All northings are 2 cm (1 km) apart
Each grid square measures
2 cm X 2 cm OR
1 km X 1 km =
1 sq. km

3. How do we measure the area?
Count the number of grid squares (n)
Area = n sq. km

4. Example 1 Calculate the area enclosed within eastings 26 and 29
and northings 58 and 62.
Solution
Eastings difference (p) = 29 – 26 = 3
Northings difference (q) = 62 – 58 = 4
Area enclosed = p X q
= 3 X 4
= 12 sq km

5. Visual method 63 24 25 26 27 28 29 30 62 61 60 59 58 57

6. Visual method 63 24 25 26 27 28 29 30 62 61 1 2 3 60 4 5 6 59 7 8 9 58 10 11 12 57

7. Example 2
Calculate the extent of cultivated area enclosed within eastings 43 and 49 and northings 85 and 89.
CWrong Solution
Eastings difference (p) = 49 – 43 = 6
Northings difference (q) = 89 – 85 = 4
Area enclosed = p X q
= 6 X 4
= 24 sq km

8. So, what is the correct solution?

9. Visual method 90 42 43 44 45 46 47 48 89 88 87 86 85 84

10. Correct solution Area enclosed by full grid squares (f)
Area enclosed = f X 1
Area enclosed by half grid squares (h)
Area enclosed = h X ½
Area enclosed by more than half grid squares (m)
Area enclosed = m X 2/3
Area enclosed by less than half grid squares (l)
Area enclosed = l X 1/3

11. TOTAL AREA
Total area
f X 1 +
h X ½
m X 2/3
l X 1/3

12. Correct solution - Visual method90 42 43 44 45 46 47 48 89 l m h 88 f 87 86 85 84

13. TOTAL AREA Total Area = 18.34 sq. km Finding the total area
f X 1 = 10 X 1 = 10 sq. km +
h X ½ = 4 X ½ = 2 sq. km +
m X 2/3 = 7 X 2/3 = 4.67 sq. km +
l X 1/3 = 5 X 1/3 = 1.67 sq. km =
Total Area = sq. km

14. REPRESENTING HEIGHTS ON TOPOGRAPHICAL MAPS

15. How are heights measured?
Start from mean sea level
Determine the heights using theodolite (principles of trigonometry)
Use these heights as bench marks to determine further heights

16. Types of heights
Triangulated Height
Spot Height
Relative Height

17. Triangulated Height Determined using principles of trigonometry
Accurate
Expressed on maps using a ∆
For example, ∆ 224

18. Prominent Surveyed Tree
Triangulated height written on tree bark
Tree is shown in black colour-
For example

19. Bench Mark Triangulated height written on nearby rock or wall
Shown using BM
For example, BM 403

20. Spot Height Height estimated using the value of adjacent contours
Shown with a dot
For example, .544
560
540
.544

21. Relative Height Height (depth) of a feature relative to surroundings
Shown using r
For example, 20r

22. Example of relative heights
Symbol
Meaning
Relative height of river bank is 7 metres
Relative height of Sand Dune is 11 metres
Relative height of Tank Embankment is 14 metres
22r
Relative Depth of Well is 22 metres 7r
11r
14r

23. End of Presentation