Descriptive and prescriptive modeling are here proposed to devise general and comprehensive Spatial Information Systems, which broaden the role of spatial data modeling from relatively passive inquiry to much more active intent. Descriptive modeling corresponds to a bottom up approach to spatial data organization, and provides tools to extract prominent features from the low level geometric model. Prescriptive modeling involves two aspects: exploration and generation. Exploration of a high level description of spatial data is performed to allocate stated geographical configurations, while the generation of low level descriptive models supports the simulation of geographical phenomena. An implementation of the proposed system architecture is presented with examples of both descriptive and prescriptive modeling in the context of digital terrain modeling.