The Nature of Georeferenced Data

Abstract

Georeferenced data or spatial data (we use the terms interchangeably here) come in many forms. Geometrically speaking, such data refer either to points, lines or areas – spatial objects or features. Spatial interaction data record flows between the nodes (intersection points) of a network. These data are captured in an origindestination matrix where the number of rows and columns of the matrix correspond to the nodes of the network and the entry on row i and column j records the total flow from node i to node j (Fischer 2000). Spatial tracking data records the movement of individuals (or groups) over time between areas or the nodes of a network (Goodchild 1998; Frank et al. 2001). The rows of the tracking matrix are the individuals, the columns are time periods and the entry on row i and column j records the location of individual i in time period j. These data can be used to estimate transition matrices where the entry on row i and column j of the transition matrix records the probability of any individual going from area i to area j in an interval of time (Wilson and Bennett 1985, pp.107-109 and pp.250-280). In these two cases the spatial objects (nodes, network links, areas) remain fixed – and motion takes place over this static spatial backdrop – but over time the point, line and area features themselves can for example move, grow, shrink, split and change form (Frank 2001).