Co-ordinate systems

Question 1

y and x

Answer 1

latitude (y) and longitude (x) co-ordinates

Question 2

what are latitude and longitudes measurements of?

Answer 2

geographic co-ordinate system

Question 3

what is longitude?

Answer 3

measured angle subtended from the centre of the earth to the surface of the earth, east and west of the greenwich meridian - prime meridian (0)

Question 4

longitude values range from?

Answer 4

180degrees E to 180 degrees W

Question 5

what is latitude?

Answer 5

anfle subtended from the centre of the earth North and south of the equator (0)
from North to south.

Question 6

latitude values range from?

Answer 6

90N to 90S

Question 7

Define the graticule.

Answer 7

A planar grid system of intersecting latitude and longitude lines.

Question 8

how to the positives and negative of longitude and latitude change with the position around the equator and greenwich meridian?

Answer 8

NW- +latitude -longitude
SW- -latitude -longitude
NE- +latitude +longitude
SE- -latitude +longitude

Question 9

how do we convert DMS to DD?

Answer 9

(degree + min/60 + sec/3600)

NB 1degree =60min
60 min = 3600sec

Question 10

what is problem with the shape of the earth?

Answer 10

oblate spheroid - need to make a model of earth to be able to meausure it.

Question 11

what is a model?

Answer 11

a simplified idealised representation of reality

Question 12

What are the 3 surfaces to consider, deciding on the best model for earth?

Answer 12

True earth surface
Geoid (mean sea level)
ellipsoid

Question 13

What is the ellipsoid model?

Answer 13

Mathematical represenation of the earth
reference for depicting geographical co-ordinates
a - equitorial axis
b- from poles the centre.

different ellipsoids work better to depict different parts of the earth.
Not a universal model.

Question 14

What is a datum?

Answer 14

mathematical model of the Earth
erves as a reference for calculating the geographic
coordinates of a location.

A datum consists of two components:
1. A reference ellipsoid
2. A reference point or location
The further the distance of a location from the reference point of
a datum on an ellipsoid, the greater the geometric distortion of
those geographic coordinates

Question 15

What was the old datum for South Africa?

Answer 15

Cape Datum
Modified Clarke 1880 reference ellipsoid
Initial point - Buffelsfontein, PE

Question 16

What is the current datum for South Africa?

Answer 16

Hartebeeshoek94 Datum
WGS84 reference ellipsoid
initial point - Hartebeeshoek, Pretoria

Question 17

Summary - conclusion

Answer 17

The further the distance of a location from the reference point of
a datum on an ellipsoid, the greater the geometric distortion of
those geographic coordinates
GIS and maps use planar projections which allows for distance and area calculations.