Mapwork Basic Skills.ppt
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Transcript of Mapwork Basic Skills.ppt
Types of spatial information
From…
A Methodology to consider
…photograph…
…to orthophoto map…
…to
topographic map
What is a photograph?A detailed and complete picture of a section of reality.
Types of photographs
• Horizontal or terrestrial
• Satellite Image
• Aerial Photography
Photographs
Aerial Photographs
Aer
ial
Ph
oto
gra
ph
s
Vertical
High (horizon )
Oblique
Low (horizon x )
Aerial photography
Cape Town1926 1996
Historical Documents
To orientate yourself is to establish your position
• “oriens” (Latin) - rising of the sun or east
• find distinctive landmarks andcorrelate photograph with actual landscape
• orientation in terms of direction - cardinal points of the compass
• in South Africa shadows fall to the south
Orientation
N
S
EW
NW NE
SESW
Direction
Direction
What is a map?A map is a generalised and reduced representation of (a portion of ) the curved surface of the earth on a flat surface
Orthophoto Map• a combination of an aerial
photograph and a map• a rectified image and true to scale
Orthophoto Maps
How does the orthophoto map differ from the vertical aerial photograph?
• A letter or symbol indicating a particular feature
What is a conventional sign?
Conventional Signs (1)
Point Line Area
Conventional Signs (2)
Making it easier:
Distinguish between two types of landscape:
• the natural / physical landscape
• the constructed / human landscape
• Five colours
- Brown- Blue - Green- Black- Red
Symbol
Brown
Symbol
Blue
Symbol
Green
Symbol
Red
Symbol
Black
• Contours
• Trig. Stations
• Spot Heights
• Bench Marks
Representation of Height
Slopes
1
1 -
22 -
Concave
Convex
Convex and Concave slopes
Equator (0°)
Northern Hemisphere
Southern Hemisphere
North Pole (90° N)
South Pole (90° S)
Latitude
West
ern
Hem
isp
here
East
ern
Hem
isph
ere
Gr e
enw
ich
Meri
dia
n 0
°
South Pole (90° S)
North Pole (90° N)
Longitude
East
ern
Hem
isphere
West
ern
Hem
isphere
Northern Hemisphere
Southern Hemisphere
S;E
Latitude & longitude
A B
C D
A B
C D
A B
C D
18° 00’
18° 00’
34° 00’ 34° 00’19° 00’
19° 00’35° 00’ 35° 00’
30’
30’15’ 45’
15’
45’
3418
1° = 60’
1° Square
Reference numbering – 1:50 000
18° 45’34° 00’
19° 00’
34° 15’
03’
51’ 54’ 57’
06’
09’
12’
48’
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
Reference numbering – 1:10 000
A
C D
A B
C D
18° 00’34° 00’
B
•1° = 60’
•1’ = 60” 30”
20”10” 40”50”
30”
10”
20”
40”
50”
01’
46’ 26° 46’ S;
29° 01’ E
26° 45’ 12” S;29° 00’ 41” E
Co-ordinates: from ° to ‘ to “
Metres
1 000
Kilometres
0 1 2 3
Line Scale
A
B
1:50 000
• This is a mathematical wayof 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
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 000100 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 000orthophoto
map 10 000
Converting cm to km
3,7 x 10 000100 000
= 0,37km or 370m
E.g. 3,7 cm on the orthophoto map
Finding north
Trigonometrical Station
Bench mark