USING HIGH-RESOLUTION LIDAR FOR GEOMORPHIC AND STRATIGRAPHIC MAPPING OF THE COASTAL PLAIN AT A SCALE OF 1:8000, SURRY PALEOSHORELINE COMPLEX, NORTH CAROLINA
Until 2018, the STATEMAP Program, funded by the National Cooperative Geologic Mapping Act (NCGMP), required map deliverables to be produced at a scale of 1:24,000. Typically, geologic data is displayed on a basemap that is a GEOPDF of a 7.5 minute quadrangle; these incorporate elevation contours and other geographic data. Contour intervals (CI) are 5 or 10 ft in Coastal Plain areas. Although a 5 ft CI is a step up from the 2 m CI on many post-1980, 7.5 minute quadrangles, higher resolution elevation data matched with orthoimagery is better suited for mapping Quaternary depositional systems on the Coastal Plain. As of 2018, the STATEMAP Program now accepts other non-traditionally scaled maps as deliverables. Demonstrated here is an example of a 1:8,000 scale map prepared for a Coastal Plain quadrangle.
After Hurricane Floyd in 1995, North Carolina acquired a continuous grid of high-resolution LiDAR elevation data for the entire state: its maximum horizontal resolution is 20 cm. For a 4 quadrangle map area on the Coastal Plain that straddles the Early Pleistocene Surry Paleoshoreline Complex, the bare earth LiDAR elevation grid was utilized to create the derivative layers using ARCGIS, Spatial Analyst and 3D Analysis: hillshade, slope and contour lines (1 m, 0.5 m and 0.25 m). Instead of using 1:24,000, GEOPDFs as basemaps, a GIS map document that included multiple layers—especially gridded elevation data, slope, 0.25 m contours, and orthoimagery—is used as a ‘base’ for a ‘comprehensive landscape analysis’ of Quaternary landscapes. To resolve specific landforms and their boundaries, layers are turned on/off as needed, and interpreted features are digitized at a range of scales, commonly 1:1,200 to 1:400 ft in complex alluvial areas.