The map projection calculates is responsible for transforming map coordinates to pixel coordinates and backwards.
The most simple example is a squared world map, thats projected with mercator transformation. Ranging from Longitude -180 to 180 and Latitude from -90 to 90 (Exclusive, because mercator gets infinite at +/-90).
Coordinates:
Often we don't use the whole map, or our map is a subsection of the world. MapProjection can clip those cases, using the a bounding box of min and max coordinates.
Coordinates:
Maps can be also translated, if the whole world is shown and clipping is not an option.
Coordinates: