ABSTRACT
Circumscribing a set of points in the plane or covering the area created this way may be of interest for several applications. We might need to construct a boundary for various purposes: to recognize the area under surveillance in a military zone, to circumscribe an infected region in the medical field, to identify a fire zone, etc. In this chapter, we put forward some definitions that we deem necessary for the understanding of the subsequent chapters. The ‘envelope’ (or ‘hull’), for instance, is a concept commonly used for the description of a set of disconnected points.
