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Historical Documents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