When creating a geospatial application, the data you use will be just as important as the code you write. High-quality geospatial data, and in particular base maps and imagery, will be the cornerstone of your application. If your maps don't look good, then your application will be treated as the work of an amateur, no matter how well you write the rest of your program.

Traditionally, geospatial data has been treated as a valuable and scarce resource, being sold commercially for many thousands of dollars and with strict licensing constraints. Fortunately, as with the trend towards "democratizing" geospatial tools, geospatial data is now becoming increasingly available for free and with little or no restriction on its use. There are still situations where you may have to pay for data, for example, to guarantee the quality of the data, or if you need something that isn't available elsewhere, but it is now usually just a case of downloading the data you need, for free, from a suitable server.

This chapter provides an overview of some of these major sources of freely-available geospatial data. This is not intended to be an exhaustive list, but rather to provide information on the sources which are likely to be most useful to the Python geospatial developer.

In this chapter, we will cover: