December 16, 2010
These Digital Elevation Model (DEM) files were created with ArcGIS v.10 from 1/3-arc-second elevation data obtained from USGS's seamless data server. The source metadata are available on the USGS website. The 1/3-arc-second data support a nominal raster cell resolution of 10 meters. The elevation (Z) values are in meters.
I mosaicked eleven USGS 1x1-degree tiles covering southeastern PA, NJ and the Delmarva Peninsula in a UTM (NAD 1983) zone 18 coordinate system. I then exported 10-meter resolution DEM's covering each of Delaware's three counties in a DE State Plane NAD 1983 HARN (meters) coordinate system. Negative values in the source data have been converted to zeroes.
These DEM's represent a significant improvement over the 30-meter resolution DEM's created by SpatLab and distributed on this website since 1999. While the older DEM's have integer elevation values in feet, resulting in discernible step artifacts in flat terrain, these DEM's have floating-point values and are smoother. They are distributed by county as compressed Arc layer package (.lpk) files. While they are substantially larger than the 30-meter-resolution composited county DEM's served from this website, they will support higher-resolution terrain and hydrologic analysis. Each layer package includes conventional elevation symbology.