ABSTRACT
Kate Beard Department of Spatial Information Science and Engineering, University of Maine,
Orono, USA
4.1 Introduction Initially geographic information systems modelled geographic features and the relations among them under the assumption that such features were independent of time. A rationale for this perspective is that many geographic features retain their identity and location for long periods of time. Given the persistence of these fundamental properties, representation of change was not an initial consideration for geographic information systems. Additionally, early spatial data collection methods (primarily photogrammetry) focused on capturing these fundamental properties: identity and location, but were generally too expensive to repeat with a frequency that could support interesting change analysis. More recent GIS research has begun to address models for representing the dynamic and mobile components of geographic features. What has remained constant, however, is that geographic layers or features are the central units of analysis and GIS operate on these units. In an event-based approach geographic features or locations are not the primary focus. This chapter describes an event-based approach in which change itself is the central concept that is modelled and change units are the principal objects and units of analysis. In this event-based approach the time dimension dominates the spatial dimensions as the ordering of events in time is critical. Because the principal unit of analysis and the organising dimension are fundamentally different, new approaches are needed for change objects. Section 4.2 of this chapter discusses previous eventbased models and approaches that have appeared in the literature. Section 4.3 presents a categorisation of change, Section 4.4 describes the proposed event model, Section 4.5 describes sources of events, Section 4.6 outlines a method for event visualisation and exploration and Section 4.7 concludes the chapter with a summary and future research challenges.
