Alle burde kende til det, men de færreste husker på det ... /Sik All should know but most tends to forget ... /Sik
Quote Written by Richard Marsden
[...] Most online map services use geographic longitude,latitude coordinates on the WGS84 datum using a Mercator Projection. Although the coordinate system and datum are both logical choices for global mapping, As you shall see, Mercator is a poor choice of projection for most map applications.
So what are these different datums, coordinate systems, and projections? Why should we care?
There are three components to representing the Earth's surface on a flat map:
Datum: This represents the shape of the Earth
Projection: This converts the curved shape of the Earth's surface into a flat map.
Coordinate System: This identifies points on the Earth's surface (and map) using (typically) two numbers.
First, we shall look at different projections. The second half of the article will cover datums and some actual coordinate systems. [...]