For most of this chapter, we'll use ASCII Grid files, or ASCIIGRID. These files are a type of raster data that's usually associated with elevation data. This grid format stores data as text in equal-sized square rows and columns with a simple header. Each cell in a row/column stores a single numeric value, which can represent some feature of terrain, such as elevation, slope, or flow direction. The simplicity makes it an easy-to-use and platform-independent raster format. This format is described in the ASCII Grids section of Chapter 2, Learning Geospatial Data.
Throughout this book, we've relied on GDAL, and to some extent, even PIL, to read and write geospatial raster data, including the gdalnumeric module, so that we can load raster data into NumPy arrays. ASCII Grid allows us to read and write rasters using only Python or even NumPy...
