General coordinate systems

Coordinate systems are used to identify locations on the Earth's surface i.e. they provide a common frame of reference. The usual coordinate systems use in a GIS are plane, orthogonal cartesian coordinates. These are orientated conventionally ie north-south and east-west. Lines of longitude or the east-west position are related to the Greenwich meridian and lines of latitude or the north-south position are related to the equator.

The earth's surface is not flat but is almost spherical. In fact it is flattened at the poles so ellipsoids are used for mapping the true curved surface of the earth.

http://www.geog.ubc.ca/courses/klink /gis.notes/ncgia/u26.html#UNIT26 This will provide further information on what is meant by general coordinate systems. You can think about the discussion and exam questions but you do not need to answer them.