Computational geometry

Computational geometry encompasses the algorithms needed to perform operations on vector data. The field is very old in computer science; however, most of the libraries used for geospatial operations are separate from computer graphics libraries because of geospatial coordinate systems. As described near the end of Chapter 1, Learning Geospatial Analysis with Python, computer screen coordinates are almost always expressed in positive numbers, while geospatial coordinate systems often use negative numbers when moving west and south. The Turtle graphics module used in the SimpleGIS example in Chapter 1, Learning Geospatial Analysis with Python, does use negative coordinates when moving left or down from the center of the canvas. This feature makes converting from world to screen coordinates a little easier, but is not typical of computer graphics libraries.

Several different geospatial libraries fit into the category but serve a wide range of uses from spatial selection...