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Digital Mapping Techniques '98 -- Workshop Proceedings
U.S. Geological Survey Open-File Report 98-487

Washington State's 1:100,000-Scale Geologic Map Database: An Arc/Info Data Model Example

By Carl F.T. Harris

Washington Division of Geology and Earth Resources
P.O. Box 47007
Olympia, WA 98504-7007
Telephone: (360) 902-1453
Fax: (360) 902-1785

Over the last 15 to 20 years, the role of the cartographer has expanded from making maps to creating relational databases, thereby broadening the use of maps as analytical tools. The discipline has moved away from creating historical documents and moved toward creating data sets that represent the most current spatial and temporal relations. These complex relations are best represented and accessed with the aid of computer hardware and software. In the field of cartography, this equipment is known as a Geographic Information System (GIS).

The power of a good GIS is not that it can generate a map but that it can be queried to find answers to complex questions. The Division of Geology and Earth Resources (DGER) has long recognized the potential of GIS technology as a tool for geologic investigation. In 1994, DGER began working toward the goal of 1:100,000-scale digital geologic coverage under a contract from the Washington Department of Ecology. The contract gave us the financial means to develop a GIS data model that would accommodate all of the Division's 1:100,000-scale geologic maps. Digital versions of two of these maps were produced as deliverables under this contract. These two maps, Priest Rapids and Richland, were a pilot project to determine the feasibility of continuing with data entry on the 50 remaining quadrangles in Washington.

With financial support from the STATEMAP component of the National Cooperative Geologic Mapping Program administered by the U.S. Geological Survey (USGS), we have been able to continue with this project. DGER has completed 29 quadrangles and has financial support to finish 11 more quadrangles by June 30, 1999. We are projecting digital conversion for all 1:100,000-scale geologic maps by June 30, 2000.

It took about 34 months of cartographer and geologist time to finish the 29 digital quadrangle maps completed so far. This includes about 6 months of geologist time to prepare materials for digitizing, convert polygon unit labels to a new standardized statewide nomenclature, and review draft products. The GIS Manager concentrates on system development, database design and integrity, training others in the use of GIS technology, problem solving, application software programming, and overall quality control. The cartographers focus on digitizing, attributing, editing, and error correction. The geologists perform data input, but are also responsible for ensuring the geologic integrity and correctness of the database.

The focus of this project has been on the production of a geologic database in Arc/Info coverage format, not on digital cartography. We have discovered that if the database is well constructed, the cartography can be applied to the database to produce map products. If we had focused on the cartography up front, the database may have been limited to only generating hardcopy output. Each map is a composite of several topologically integrated coverages. Each set of similar map features is awarded its own coverage and unique set of attributes. Depending on the complexity of the geology in a given area, a quadrangle may be composed of a few or several coverages.

The source geologic maps for this project were prepared manually using scale-stable copies of published USGS 1:100,000-scale topographic quadrangle maps as base maps. For most maps, geologists drafted the geologic information onto Mylar overlays that were photographically composited with the base maps to produce master geologic maps on Mylar; these were copied for distribution as open file reports by running them through an Ozalid machine. In a few cases, we have obtained digital line work from the USGS to convert and incorporate into our database. At a minimum, a change to DGER geologic unit nomenclature is required to incorporate these files. The 1:100,000-scale quadrangle boundaries were taken directly from the corporate GIS database of our parent organization, the Washington Department of Natural Resources (DNR), who acquired them from the USGS. DGER used this base to assure GIS integration with data from DNR as well as federal agencies. The coastline was digitized directly off the USGS topographic map to ensure a faithful replication of the original source map. All other open water features were captured directly from the USGS 1:100,000-scale DLG and enhanced by hydrographic data from the USGS quadrangles captured by DNRs Resource Mapping Section.

We believe the most important task of a state geological survey is to keep the state geologic map up to date and readily available in its most useful form. Good geologic maps are essential to a states economic development, hazard assessment, and aid in the protection of ground water and other environmental assets. We are pleased to be able to make this information available to the citizens of Washington.


The spatial information in the geology GIS database is comprised of the 10 topologically integrated ARC/INFO coverages listed below. Additional tabular information pertaining to lithology, map authorship, and feature names is contained in several INFO files that relate to the coverages through the use of primary and secondary keys.

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Last updated 10.06.98