ABSTRACT
This chapter focuses on spatial relationships, with an emphasis on 3D topology. Topology has proved to be a useful tool in the management and analysis of digital spatial data, for the definition of spatial relationships, and for the maintenance of consistency. Accuracy means the difference between the value recorded for a measurement, and the ideal value that would be recorded if no errors or limitations on the measurement had occurred. Using interchange protocols such as Geography Markup Language the transfer of coordinate values is in decimal numbers with finite precision. This means that the consistency of the data can, and does, change as a result of the transmission. The union and intersection operations in many implementations may not be associative. The calculation of topological relationships between objects is also trouble-prone. The difficulty of operations on data from different sources is discussed in Burrough and McDonnell.
