Basic Map work skills Scale Ratios Area Profiles Gradient

1. Geographical Techniques

2. The concept of scale…

4. Written / Word scale
Ratio Scale or Representative Fraction
Graphic Scale (Line Scale)
1cm represents 0,5kms
Types of Scales

5. Metres
1 000
Kilometres
0 1 2 3
Line Scale
A
B

6. 1:50 000
• This is a mathematical way
of expressing the scale
• Only numbers are used and it refers to
the same unit of measurement
Numerator
• The numerator is always 1
& represents the map
Ratio Scale
Denominator
• The denominator is always bigger
& represents the ground

7. map distance in cm ground distance equivalent i.e. 50 000
100 000
E.g. 3,7 cm on the
topographic map
3,7 x 50 000
100 000
= 1,85 km
• To convert cm to km you must divide by 100 000 (1km
= 100 000 cm)
• Converting distance on the 1:50 000
topographic map:
x
1:10 000
orthophoto map
10 000
Converting cm to km
18,5 x 10 000
100 000
= 1,85km
E.g. 18,5 cm on the
orthophoto map

8. Something to do…
Measuring distance

9. Calculating area

10. Calculating area
1 ha = 100 m x 100 m
1 mm repr. 50 m
2 mm repr. 100 m

11. Something to do…
Calculating area

12. Cross-section / Profile

13. A
B
0 – Sea Level
200
Cross-section / Profile 1
Trig. Station
Secondary Road
N2
Dam
Dam

14. Vertical Scale: 1:10 000 (1mm = 10m)
Cross-section / Profile 2
Horisontal Scale: 1:50 000

15. 1 mm = 10 000mm
1 mm = 10 metres ( and 1metre = 1 000mm)
1 mm = 10 x 1 000 mm
1:10 000
Vertical scale

16. Vertical Scale (cross section)
Horizontal Scale (map)
VE =
1
10 000 X
50 000
1
=
1
10 000
1
50 000
=
5 times
=
Vertical exaggeration

17. Gradient

18. What is gradient?
It is the relationship between:
• how high you have climbed, and
• how far you have walked on a horizontal plane
Gradient is expressed as a ratio:
Vertical distance : Horizontal distance
Slopes are not perfectly even, so it is more correct
to refer to the average gradient.
Gradient (1)

19. Gradient (2)

20. A
B
40m
8,2cm
Gradient expressed as a ratio:
Vertical distance : Horizontal distance
c
240m
3,6cm
Gradient (3)

21. Vertical distance : Horizontal distance
40m - 0 = 40m : 8,2cm (1cm represents 0,5km)
40m : 4,1km
40m : 4 100m
(1km = 1 000m)
102,5
1 :
40m
40m
:
4 100m
40m
280m - 40m = 240m : 3,6cm
240m : 1,8km
240m : 1 800m
1 : 7,5
240m
240m
:
1 800m
240m
Comparison:
AB 1 : 102,5 BC 1 : 7,5
Gradient (4)