7.1 Introduction

This chapter is about reading and writing geographic data.Geographic data import is essential for geocomputation: real-world applications are impossible without data.For others to benefit from the results of your work, data output is also vital.Taken together, we refer to these processes as I/O, short for input/output.

Geographic data I/O is almost always part of a wider process.It depends on knowing which datasets are available, where they can be found and how to retrieve them.These topics are covered in Section 7.2, which describes various geoportals, which collectively contain many terabytes of data, and how to use them.To further ease data access, a number of packages for downloading geographic data have been developed.These are described in Section 7.3.

There are many geographic file formats, each of which has pros and cons.These are described in Section 7.5.The process of actually reading and writing such file formats efficiently is not covered until Sections 7.6 and 7.7, respectively.The final Section 7.8 demonstrates methods for saving visual outputs (maps), in preparation for Chapter 8 on visualization.