Digital database of the previously published Geologic Map of Alabama (Special Map 221)

A digital version of the 1:500,000 scale geologic map of Alabama (Osborne and others, 1989) was required for a new national compilation of state geologic maps and U.S. Geological Survey regional maps, but the map had not previously been digitized. The USGS National Cooperative Geologic Mapping Program’s (NCGMP) National Geologic Synthesis Project worked with the Geological Survey of Alabama (GSA) to digitize the map in the NCGMP’s Geologic Map Schema (GeMS) format. The GSA provided an image of the map, which the USGS team georegistered and used as a base to digitize the vector lines and populate the nonspatial tables. Once the map content was encoded in a GeMS database, the GSA reviewed the map and provided corrections to both the vector lines and text content in the nonspatial tables, primarily the descriptions of map units. The content of this database is as faithful as possible to the original 1989 printed map. When displayed using the FGDC Digital Cartographic Standard for Geologic Map Symbolization (USGS Techniques and Methods 11-A2, 2006) it closely approximates the lines symbols and colors of the original map.