ABSTRACT
Geographical computing is based on the digital representation, in spatial databases, of geographical features and distributions. Many of the features shown on maps, for example lakes, roads, and human settlements, are conceptualised as discrete objects and are readily represented as such in spatial databases. Land surveyors and photogrammetrists are particularly interested in such well-defined features, which are readily mapped and added to spatial databases as discrete objects with associated geometry, and with attributes derived from qualitative or quantitative descriptions. Such objects are important not only on their own merits, but also for the functions they can perform in co-registering data layers. It has been shown in earlier chapters that the positional and attribute components of spatial objects can be discussed separately, thus explaining the emphasis that is often placed on positional data for discrete objects. Many geometric and topological operations can be performed on objects, by analysing points, lines, and areas with respect to neighbourhood, intersection, and containment.
