Introducing PostGIS

In this book, we will be working with PostGIS. PostGIS is one of the most popular and powerful geospatial databases and has the bonus of being open source and freely available. PostGIS itself is actually an extension to the PostgreSQL relational database system—to use PostGIS from your Python programs, you first have to install and set up PostgreSQL, then install the PostGIS extension, and then finally install the psycopg2 database adapter for Python. The following illustration shows how all these pieces fit together:

Tip

Note that PostgreSQL is often referred to as Postgres. We will regularly use this more colloquial name throughout this book.

PostGIS allows you to store and query against various types of spatial data, including points, lines, polygons, and geometry collections. PostGIS provides two different types of spatial fields that can be used to store spatial data:

• The geometry field holds spatial data that is assumed to be in a projected coordinate system. All calculations...