The Geologic Mapping Act of 1992 and its subsequent reauthorizations mandate the development of a National Geologic Map Database and the standards necessary to support its implementation. The database effort is multifaceted and, in part, is intended to provide public access to digital geologic maps and associated information. The U.S. Geological Survey (USGS) and the Association of American State Geologists (AASG) are cooperatively building this database; this work includes the design and testing of the requisite conceptual and physical data model, and development of a standard science language for describing geologic features. The work described here is being led from within the USGS National Geologic Map Database project (ncgmp.usgs.gov/ngmdbproject), and is coordinated with related activities in the Federal Geographic Data Committee and the North American Data Model Steering Committee. The database project has undertaken a series of prototypes to construct working databases using sample data sets. The longest standing prototype uses geologic map information from Kentucky in a data model with an object-oriented design, and was implemented in GE-Smallworld database technology.

The object-oriented data model permits efficient storage of geologic information. Features from geologic maps are associated with classification concepts, have descriptive characteristics and metadata, and can be related to other database elements. The prototype was developed by analyzing existing map data for a 30 x 60 minute geologic quadrangle (composed of 32 7.5-minute quadrangles) to identify necessary database features. Standard geologic terms, their definitions, and relations were documented and preloaded into the database. Spatial features were then added and linked to the existing definitions.

Database design and integrity were tested by performing simple queries, demonstrating scale-dependant generalization, creating derivative maps using map-unit descriptions, conducting spatial analyses, and exporting results to external systems. Subsequent prototypes will advance the concepts developed here, and will begin to provide public access to the geologic database.