Adjacency and Connectivity are two fundamental spatial relationships that are used both descriptively and analytically in a wide range of spatial analyses and geographic contexts. These topologically invariant relationships have been instrumental in the development of data models for geographic information systems, most notably in the development of the vector data model. Adjacency provides a means of defining a neighborhood for the computation of many raster-based functions such as smoothing and surface flow analysis. Connectivity and adjacency also provide a means for defining neighborhoods for use in spatial statistics, and for guiding movement across transportation networks. These concepts are intrinsic to many spatial analytic techniques given that they strongly reflect the notion of spatial nearness.