5. All maps will provide you with a Arrow indicating both truth North (the precise top axis of the earth’s spheroid) and a magnetic north which indicates where our compasses will point to as north North Pole South Pole Magnetic North Pole Magnetic South Pole

6. For global represented of position we use degrees of Latitudes (parallels) and Longitude (meridians). The largest in length degree of latitude is the equator and forms the base line for measurements of degrees of latitude which increase until you reach the north or south pole at which point a right angle has been formed (hence the poles are 90 0 latitude). At 23.5 north and south latitude the tropics of Cancer and Capricorn occur respectively.

7. In contrast to these degrees of latitude which become smaller the degrees of longitude inscribe the same-sized circumferences but do not lie parallel to each other

9. Cylindrical projections are derived from projecting a spherical surface onto a cylinder. For example if you took you’re orange and wrapped an A4 sheet of paper around it. The paper can be arranged around the orange in a variety of arrangements A Tangent Projection would result if you wrapped your paper vertically so that the cylinder was parallel to the meridians (lines of longitude).

14. In the secant case, the cylinder touches the sphere along two lines, both small circles (a circle formed on the surface of the Earth by a plane not passing through the center of the Earth).

15. When the cylinder upon which the sphere is projected is at right angles to the poles, the cylinder and resulting projection are transverse.

17. When the cylinder is at some other, non- orthogonal, angle with respect to the poles, the cylinder and resulting projection is oblique.

18. The Mercator projection is one of the best known and has straight meridians and parallels that intersect at right angles. Scale is true at the equator or at two standard parallels equidistant from the equator. This projection seriously distorts distances and areas.

19. The Universal Transverse Mercator (UTM) is probably the best known projection system for displaying large surfaces of the earth since it provides high levels of precision. To minimize the distortion the cylinder is wrapped around the earth transversely and is place at 6 0 of rotation East and West of 180 0 meridian for each hemisphere. Consequently 60 zones north and 60 zones south are generated and are numbered eastward from the 180 0 meridian. Cape Town lies in the 34th Zone and is referred to as UTM 34S. The UTM system is only applied from 84 0 North to 80 0 South Latitude.

21. Conic projections which result from projecting a spherical surface onto a cone. When the cone is tangent to the sphere contact is along a small circle such as a latitude. You can view this by twisting your A4 sheet into a cone and placing over the orange.

22. Albers Equal Area Conic projection allows areas to be proportional and directions true in limited areas but distorts scale and distance except along standard parallels. This is one of the most common projection used to map large countries where the east-west distances are greater than the north-south extent (e.g. USA and Russia). It is often used to represent South Africa.

23. Azimuthal or Planar projections are where a flat sheet is placed in contact with a sphere, and points are projected from the sphere to the sheet. You can do this by taking your A4 sheet and pressing it against the orange.

24. NON-PROJECTIONS Plane: (Cartesian) - not a projection but truth to earth surface - data may be stored in this form, but it is not good for accurate measurements of distance e.g. metres.

25. Datums While we often refer to the earth as a sphere, it is more correctly referred to as a geoid (defined as a hypothetical surface of the earth that corresponds to mean sea level). The earth is not a sphere since it is flattened at both poles and bulges at the equator. In addition there are significant bulges and depressions on the surface. The are hundreds of different datums which have been used to estimate the size (areas and distances) of features on the earth. Datums have evolved from those describing a spherical earth to ellipsoidal models derived from years of satellite measurements.

26. To best describe this geoid mathematically, we use reference ellipsoids to approximate the size and shape of the earth.

27. Lets look at a Map - Saldanha Bay