# Projections and Coordinate Reference Systems (CRS)

Build on the fundamentals of Projections and Coordinate Reference Systems.

## Projections

It’s common to model the Earth as an ellipsoid. However, to draw the entire Earth or parts of it onto a map or a computer screen, we need a mathematical model that transforms the Earth’s curved surface onto a two-dimensional surface. This mathematical model is called a **projection system**.

There are different types of projection systems available, and each one has its own set of strengths and weaknesses, depending on the region of the Earth being mapped and the purpose of the map. The two most common types of projections are:

Cylindrical

Planar

These types of projections are presented below.

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