The representation of complex spatial domains in conventional databases suffers from fragmented representation of object structure, lack of instance-level spatial relationships, and the generation of large combinatoric search spaces in query analysis. The deductive capabilities provided by a deductive database offer some assistance in solving these problems, in particular by enabling spatial reasoning to be performed by a Geographic Information System (GIS). Deduction in the database is used to support the natural representation of complex spatial object structures in single and multi-layered Geographic DataBases (GDB), inference of implicit spatial relationships, and the manipulation of multiple resolution spatial representations. In addition, deductive capabilities are shown to be essential for automatic data input and update in a GDB. Coupled with appropriate structural representation, spatial reasoning is an important tool for the realization of an effective GDB.