This set of 1-foot contours were derived from a 2014 LIDAR DEM flown for the state of Delaware using a modified version of the USGS Contour Derivation algorithm detailed by Arundel et al. (2017),. Details for the LIDAR flight may be found in the report by Quantum Spatial (2015) linked below.
Contours are indexed at 5-foot intervals and classified as “Normal” or “Depression”. Contours are projected in Delaware State Plane NAD83 (2011) meters and the vertical datum of the source DEM was NAVD88. These contours are derived from the bare-earth 2014 LIDAR Digital Elevation Model (DEM) surface but are adjusted to conform to features in the National Hydrologic Dataset (NHD) for the purpose of generating aesthetically pleasing maps and figures from the GIS-derived contours. Visual inspection, smoothing, and manual editing were performed. Major edits included smoothing contours along some coastlines and coastal inlets to remove jagged looking artifacts created by the contouring algorithm and manually adjusting contours along the Lower Marshyhope River. Minor edits included some adjustments to depression classifications, removal of depression contours within water bodies, and removal of extremely small contour fragments along some quad boundaries. To reduce file sizes, nodes were spaced such that contours appear smooth at 1:2400 scale and lower, but finer scales may appear angular.
Accuracy of elevation contours can be based on the accuracy of the individual LiDAR points. Acquisition of the 2014 LiDAR met Quality Level 2 specifications with a sampling density of greater than 2 points per square meter and an open terrain vertical accuracy of 6.3 cm. Errors were higher in heavily vegetated areas (i.e., tall grasses, forests). See Airborne Topographic LiDAR Report: Sandy Delaware and Maryland technical report by Quantum Spatial (2015). for more details.
Elevation contour data are available for download:
Contour map layers are also available through Delaware FirstMap
Details on the 2014 LiDAR acquisition, processing steps, development of the bare-earth elevation model (from which the contours were derived), and overall assessment of the 2014 LiDAR products can be found in the following report:
- Airborne Topographic LiDAR Report: Sandy Delaware and Maryland technical report by Quantum Spatial (2015).
Details on the employed USGS contouring algorithm are described in the following article:
- Arundel, S.T., Thiem, P.T. and Constance, E.W. 2017. Automated Extraction of Hydrographically-Corrected Contours for the Conterminous United States: The U.S. Geological Survey US Topo Product. Cartography and Geographic Information Science, 1-25. http://dx.doi.org/10.1080/15230406.2016.1230027
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