THE DEVELOPMENT OF DIGITAL AND FIELD-BASED SURFICIAL AND BEDROCK MAPPING TECHNIQUES AT THE 1:100,000-SCALE IN VIRGINIA

The Virginia Department of Energy (Virginia Energy) began digitally compiling 1:100,000-scale (100K) maps in 2020, focusing on the Valley and Ridge and Blue Ridge provinces. Compiling data at the 100K-scale posed challenges to our mapping team, including how to incorporate previous mapping at various scales, integrating differing interpretations of the surficial and bedrock geology, and creating a system of packaging data that allows for consistency in each map product.

Virginia Energy has submitted 14 GeMS compliant 100K open-file report maps through the National Cooperative Geologic Mapping Program. These maps were some of the first that we created using the U. S. Geological Survey GeMS (Geologic Map Schema) standard. To generate a map product that is representative of both the modern and legacy mapping efforts, we developed a series of guidelines that prioritize which map data to include. It is an iterative process that our survey is continuing to improve upon.

Each map has unique requirements. The Buena Vista and Charlottesville 100K maps required new bedrock mapping to occur in tandem with surficial mapping. Maps like Danville, Front Royal, and Roanoke had published 100K bedrock maps but required new surficial mapping. With these complexities in mind, we began gathering existing data to identify where there were data gaps. Areas with recent mapping and those with existing GIS data were prioritized. Geologically complex areas and those with multiple scales of mapping (e.g. 1:24,000, 1:100,000, county-scale) were identified and evaluated by the mapping team and then compared to LIDAR and topographic basemaps to help create a draft interpretation. Utilizing a 5-meter LiDAR DEM, we digitized line and polygon features in GIS while zoomed in to a maximum resolution of 1:10,000, and only included features visible at 1:50,000. These constraints create consistency across a large mapping area and assist with deciding which surficial deposits to keep and where bedrock linework can be simplified. Once a draft map is made, field verification of surficial deposits and, when necessary, bedrock outcrop can begin. Updates made based on field observations and further discussion with the mapping team result in a draft geodatabase that is reviewed for geologic accuracy and GeMS compliance.