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Aggregation hierarchies for multiple scale representations of hydrographic networks in GIS.

An important aspect of the representation of terrain objects in GIS is the level of geometric and thematic detail, which is related to the scale of the terrain description. Different sets of elementary objects may exist at different scale or aggregation levels within the same . thematic users context. These levels may be related by the fact that elementary objects at one level can be aggregates of elementary objects from a more detailed level, so that aggregation hierarchy structures can be defined. A conceptual model for automated generalization of hydrographic information is presented. Topological relationships are fundamental in the definition of the aggregation rules to compose complex hydrographic objects from elementary objects. The Formal Data Structure for single vector structured maps as proposed by Molenaar [2] is used to model terrain data in a GIS environment. An application has been developed to obtain multiple scale representations using the combination Arclfnfo and Oracle RDBMS.