How this is done is the essence of the science of cartography. In the context of oceanography we restrict ourselves to a very brief review of the essentials. Fidelity of angle is paramount in maps used for navigation, which is based on compass bearings, i.e. the angle of the course of a ship or aircraft with respect to the magnetic north pole. The preferred map orientation is that, for all points on the map, north is up and east is right. Cartographers teach us that it is not possible to combine all these essentials in a single projection.
Different projections exist to serve different purposes.
The correct choice of map is an important part of displaying information in oceanography.