Digital Mapping Techniques '99 -- Workshop Proceedings
U.S. Geological Survey Open-File Report 99-386

A Digital Geologic Map Data Model Designed for GIS Users

By Loudon R. Stanford, Kurt L. Othberg, Reed S. Lewis, and Roy M. Breckenridge

Idaho Geological Survey
Morrill Hall, Room 332
University of Idaho
Moscow, ID 83844-3014
Telephone: (208) 885-7991
Fax: (208) 885-5826


Geologic maps are an invaluable source of spatial data about surface and subsurface geology, and are increasingly used by non-geologists. Notably, most GIS-capable agency, industry, and education units seek geologic maps and digitize or import them into their systems. Geologic maps are a challenge to understand, and many well-trained GIS analysts and technicians lack an understanding of the scientific methods behind the interpretations on a geologic map. This can lead to misuse of the data, especially when the data are in digital form.

Based on the USGS model, we are designing geologic map products that meet the needs and expertise of the GIS community. Digital geologic maps are more than digitized lines, symbols, and polygons. Without explanation, those spatial data have little value. The digital product (digital geologic map) consists of spatial databases (composed of lines, polygons, and symbols), and a digital explanation database. The digital explanation consists of a hierarchy of tables that are linked to each other and are linked to the components of the spatial database. The power of a digital explanation is giving the user the ability to "query" or search the database, and generate a derivative version of the map. For example, one can search and select parameters such as lithology, stratigraphy, origin, landform, weathering, relative age, radiometric age, and sources of data (field mapping). Authors of digital geologic maps may include other parameters such as magnetic polarity, soil series, and hydrologic characteristics. This system of organizing the scientific information that comprises a geologic map provides a new way to present geologic observations and interpretations that will aid in the educated use of these data.


The Idaho Geological Survey (IGS) is developing a derivative model based on the proposed USGS data model (version 4.2). The IGS model uses the ARC/INFO GIS spatial database as its core. IGS has several goals to achieve in the development of a Geologic Map Data Model and the user tools associated with it:

Development of the IGS model began in September 1998. Currently we have a prototype which is being modified. A prototype query engine tool has also been written.

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