In this chapter, we took an in-depth look at the PyQGIS libraries and how you can use them in your own programs. We learned that the QGIS Python libraries are implemented as wrappers around the QGIS APIs implemented in C++. We saw how Python programmers can understand and work with the QGIS reference documentation, even though it is written for C++ developers. We also looked at the way the PyQGIS libraries are organized into different packages, and learned about the most important classes defined in the qgis.core and qgis.gui packages.

We then saw how a coordinate reference systems (CRS) is used to translate from points on the three-dimensional surface of the Earth to coordinates within a two-dimensional map plane.

We learned that vector format data is made up of features, where each feature has an ID, a geometry, and a set of attributes, and that symbols are used to draw vector geometries onto a map layer, while renderers are used to choose which symbol to use for a given feature...