Topographic exposure is a variable which represents the degree of shelter afforded to a location. A detailed knowledge of exposure is useful for a wide variety of applications, ranging from the dynamics of drifting snow to the optimal location of wind-farms. The degree of exposure can be calculated by considering the relative heights and distances of the horizon surrounding the point of study. Numerous approaches have been developed to measure this useful variable, from the early qualitative studies of wind-shaped trees to Pyatts's quantitative TOPEX assessment. However, these studies have been superseded by the use of computers and in particular the application of digital terrain models. These provide a fast office-based solution, virtually eliminating the need for fieldwork.