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FIELDS AND OBJECTS ALGEBRAS FOR GIS OPERATIONS1

This paper addresses the problem of formal definition of the operations on geographical information systems (GIS). Geographical data is divided in two main classes: geo-objects and geo-fields, which portray discrete and continuous representations of reality. We study the operations over geo-fields, geo-objects, and the transformations between geo-fields and geo-objects. This analysis has been used as the basis for LEGAL, a general spatial language, which is used in the SPRING GIS, developed by INPE, with support from IBM Brazil and EMBRAPA.