Working with map projections

A map projection is used to convert data from a geographic coordinate system to a projected (planar) coordinate system. Just like there are many geographic coordinate systems, there are many different map projections as well —each preserves the spatial properties of data (shape, area, distance, and direction) differently.

Maps are always flat, so do you always need a map projection? The answer is maybe—it depends on what you want to do.

For example, suppose your project doesn't require a high level of locational accuracy—you won't be performing analysis based on location and distance or you just want to make a quick map. In these situations, there is probably no need to convert your data to a projected coordinate system.

However, if you need to perform analysis (measure distances, calculate areas and perimeters, determine the shortest route between two points) or if you need to show a particular spatial property for features on a map as it really exists on the earth, you should use a map projection to convert your data to a projected coordinate system.