Deriving topography-related variables from a DEM is a central task in terrain analysis. Many functions and algorithms have been developed for this purpose, and different GIS software packages include different sets of such tools. The raster package currently provides several basic terrain analysis functions (of which three examples will be shown in this section).
Note
A variety of terrain analysis (and other) algorithms are available in R through interfacing with open source GIS software, such as SAGA GIS (using the RSAGA package) and GRASS GIS (using the spgrass6 package). To use these, you will require to download and install the (freely available) respective software, but the subject is beyond the scope of the present book, which focuses on standalone R functionality.