GIS DATABASE FOR THE DNAG GEOLOGIC MAP OF NORTH AMERICA

In 1998, the Geological Society of America (GSA) and the U.S. Geological Survey (USGS) National Geologic Map Database project (NGMDB) agreed to cost-share the digital preparation of the Geologic Map of North America (GMNA). Development of the GMNA for final print production required digitization of various hand-drawn, author-prepared, geologic base maps. The resultant digital data allowed the NGMDB project to begin development of a prototype database. In 2005, the GMNA was printed and released as the final product of the GSA's Decade of North American Geology project (Reed, J.C. Jr., Wheeler, J.O., and Tucholke, J.E., compilers, 2004, Geologic Map of North America: Decade of North American Geology Continental Scale Map 001, Boulder, Geological Society of America, scale 1:5,000,000). In 2006, the NGMDB project began to create a Geographic Information System (GIS) compatible database. A complete GIS dataset for the southern half of the GMNA has now been prepared; it contains the descriptive information for geologic units shown on the printed versions of the GMNA. After conversion of the southern and northern sheets, the databases will undergo technical edits and be made publicly available. We anticipate this might occur in 2008.

The GIS dataset for the southern portion of the GMNA includes over 900 individual geologic map units, nearly 150 of which are offshore. It contains 72 unique feature classes, 22,000 geologic polygons, and over 50,000 geologic unit bounding line features. GIS compatible digital data were constructed from two Adobe Illustrator files, each containing over 1500 layers. Geologic unit attribution was completed via VBA scripting.

The creation of this database and its eventual enhancement to include new mapping and additional attributed information is a time and labor intensive effort. Recognizing that a group of dedicated and knowledgeable scientists is essential to make this database useful and to keep its content up to date. In the future, GSA may develop a consortium of geological agencies to manage the database. With development of the prototype database, the USGS NGMDB project will provide a basis for this consortium to proceed.