Generalisation Methods for Propagating Updates between Cartographic Data Sets
Abstract: Automation is increasingly important in producing and maintaining cartographic data sets. This thesis deals with automatic methods to propagate updates between cartographic data sets. The major idea is to update only the most detailed data set (master data set) and then propagate these updates automatically to less detailed data sets (target data sets). The approach used is firstly to formulate linguistic rules for the update process. The information sources for these linguistic rules are data set specifications, cartographic data sets, paper maps and practising cartographers. These linguistic rules are translated into logical rules and then implemented in a prototype system. The prototype system is built on top of an object-oriented map production software. The system requires a multiple representation database, which consists of cartographic data sets at different scales together with connectivities between those objects that refer to the same physical entities. The prototype system is built on a conceptual framework of four steps: examination, propagation, generalisation of updates and solving spatial conflicts. The aim of the examination step is to determine which object should be created, modified or deleted in the target data set. The action is dependent on the current status of the target data set and the properties of the update to the master data set. The propagation step executes the outcome of the examination step. Furthermore, this step validates the updates and maintains the integrity of the multiple representation database. In the next step – generalisation of updates – the new or modified object in the target data set is generalised to suit the scale of the target data set. The final step treats spatial conflicts due to the update. A new method is proposed for solving spatial conflicts, called the constraint method, which is a generic method that resembles manual generalisation on a conceptual level.
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