NEW DIGITAL GEOLOGIC MAP OF VIRGINIA COMPLETED AS A LEVEL 2 GEMS GEODATABASE

Virginia’s geological survey produced statewide geologic maps at 1:500,000-scale in 1916, 1928, 1963, and 1993. All of these maps were produced using manual compilation and publishing techniques. In 2003, the 1993 map was digitized and published in shapefile format to meet the growing demand for digital geologic data. In 2019, several factors encouraged the Virginia Department of Energy (which houses the current state geological survey) to undertake a new statewide “born-digital” geologic map: 1. About 25% of the state had been mapped or remapped at 1:24,000-scale since 1993; 2. The USGS Geologic Map Schema (GeMS) had gained traction as the standard format for digital geologic maps; and 3. Funding became available for statewide compilations through the USGS’s National Cooperative Geologic Mapping Program. In addition, the recent availability of statewide LiDAR coverage enabled the creation of a 10-meter digital elevation model (DEM), which served as a consistent statewide base. The DEM also proved to be helpful in interpreting surficial and bedrock geology in areas with sparse field observations. An ArcGIS enterprise geodatabase was designed using the GeMS schema and populated with the 1993 geology to serve as a starting point for the compilation. Each geoscientist working on the map downloaded a replica for editing locally on their desktop computers using the ArcGIS distributed geodatabase tools. Digitization protocols that included minimum lengths of structures and minimum widths and areas of polygons were established to ensure edits were consistent between editors. After making edits, geologists synchronized their data with the parent geodatabase, incrementally building the new digital map. After all polyline edits were complete, map unit polygons were created and symbolized. Throughout the process, feature attributes were populated with citation information to capture the original data sources. The 1993 expanded explanation was imported into the GeMS description of map units table and updated with additional descriptive information. The GeMS schema proved to be a satisfactory format for capturing the compilation and producing the map update. The new map is currently in review and is expected to be available as a digital web map service in the next year.