1. The National Map, elevation. [Reston, Va.] : U.S. Dept. of the Interior, U.S. Geological Survey, [2009] Book Online
2. The National Map product and services directory. [Reston, Va.] : U.S. Dept. of the Interior, U.S. Geological Survey, [2008] Book Online
3. Use of light detection and ranging (LiDAR) to obtain high-resolution elevation data for Sussex County, Delaware / by Roger A. Barlow, Mark R. Nardi, and Betzaida Reyes ; in cooperation with the Delaware Geological Survey and the U.S. Department of Agriculture Natural Resources Conservation Service. Barlow, Roger (Roger A.) [Reston, Va.] : U.S. Dept. of the Interior, U.S. Geological Survey, [2008] Book Online
4. Revision of primary series maps. [Reston, Va.] : U.S. Dept. of the Interior, U.S. Geological Survey, [2000] Book Online