Database Systems

Spatial Join and Map Overlay


One of the most important operations in relational database systems is the join operation. The corresponding operation in a spatial database system is the spatial join. The spatial join operation combines objects from two spatial relations according to geometric attributes, i.e. their geometric attributes have to fullfil a spatial predicate. Spatial predicates may be intersection, containment or distance predicates. The importance of the spatial join is comparable to the importance of the natural join in a relational database system. It can be used for the implementation of all kinds of operations and queries, which combine sets of spatial data. In a GIS system, the spatial join may be used for an efficient implementation of the map overlay. The map overlay constructs a new map from two or more given maps which is important for geographic analysis. Application areas are for example, city planning, ecological, demographic, and geophysical studies.

The goal in this research area is to develop a spatial join processor, which is also based on the concept of multi-step spatial query processing. The spatial join processor will be the basis for an efficient implementation of the map overlay. A further goal is the construction of algorithms for parallel spatial join processing. Important publications in this area are [KBS 91], [BKS 93a], [BKSS 94a] and [BKS 96].

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