Changing datums and projections

In Chapter 2, GIS, we saw that a datum is a mathematical model of the earth's shape, while a projection is a way of translating points on the earth's surface into points on a two-dimensional map. There are a large number of available datums and projections—whenever you are working with geospatial data, you must know which datum and which projection (if any) your data uses. If you are combining data from multiple sources, you will often have to change your geospatial data from one datum to another or from one projection to another.

Task – changing projections to combine shapefiles using geographic and UTM coordinates

In this recipe, we will work with two shapefiles that have different projections. We haven't yet encountered any geospatial data that uses a projection—all the data we've seen so far used geographic (unprojected) latitude and longitude values. So, let's start by downloading some geospatial data in the Universal Transverse Mercator (UTM) projection...