The orientation of terrain surface (aspect) can have dramatic effects on landscape-scale variation in soil temperature and moisture. Summarizing aspect angle is complicated by the fact that sampled values are measured on a circular scale. The circular package for R can be used to summarize, model, and visualize this type of data.
An example function is presented below that demonstrates several components of the circular package: special data structures, summary functions, plotting functions and their application to circular data derived from measurements collected by compass. Spread and central tendency are depicted with a combination of circular histogram and kernel density estimate. The circular mean, and relative confidence in that mean are depicted with an arrow: longer arrow lengths correspond to greater confidence in the mean.