A projection is a way to translate the curved surface of the earth (3D) onto a flat map (2D). The challenge is that every map projection has distortion because the spherical nature of the globe cannot be perfectly represented in a two dimensional map. The picture below illustrates similarities and differences of three map projections. This image powerfully demonstrates the importance of defining the projection. For example, if you were working with data in Washington State you may have very different results working in Mercator or Lambert Conformal Conic. Knowing the projection of your data is important especially when working with data that is part of a dataset that is larger than just your county or state.

This tasksheet will cover how to change the projection of an existing file as well as enabling on the fly projection in QGIS.