There isn't one single system, but rather several different map projections used to map the round Earth onto a flat surface. Each projection has its own strengths and weaknesses, resulting in different distortions of the Earth's shape and size.

Here are some common map projections:

* Mercator Projection: This is perhaps the most well-known projection, used for nautical charts. It preserves angles and shapes near the equator, but distorts sizes and distances towards the poles. Greenland, for example, appears much larger than it actually is.

* Robinson Projection: This projection attempts to minimize distortions by using a compromise between area and shape. It is commonly used for world maps, but it doesn't preserve angles, shapes, or areas perfectly.

* Mollweide Projection: This projection is an equal-area projection, meaning it preserves the relative sizes of continents and countries. However, it distorts shapes, particularly near the poles.

* Azimuthal Equidistant Projection: This projection preserves distances from a central point, making it useful for mapping regions centered around a particular location. However, it distorts shapes and sizes away from the central point.

These are just a few examples. Other projections exist, each with its own advantages and disadvantages. The choice of projection depends on the purpose of the map and the specific information it aims to convey.