For most of this chapter, we'll use ASCII Grid files or ASCIIGRID. These files are a type of raster data 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, platform-independent raster format. This format is described in the ASCII Grids section in Chapter 2, Geospatial Data.
Throughout the book, we've relied on GDAL and, to some extent, PIL to read and write geospatial raster data including the
gdal_array module to load raster data in the NumPy arrays. ASCI Grid allows us to read and write rasters using only Python or even NumPy because it is simple, plain text.