Accuracy is computed by a comparison of linear interpolated elevations in the DEM with corresponding known elevations. A minimum of 28 test points per DEM is required to compute the RMSE, which is composed of a single test using 20 interior points and 8 edge points. These errors are reduced in magnitude by editing but cannot by completely eliminated and may be encountered. Blunder errors are those errors of major proportions and are easily identified and removed during interactive editing. Systematic error are those errors that follow some fixed pattern and are introduced by data collection procedures and systems.
Random errors result from unknown or accidental causes.
DEMs are edited to correctly depict elevation surfaces that correspond to water bodies of specified size. Explicit elevation coordinate included with horizontal coordinates. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, National Wetlands Research Center, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that these data are directly acquired from a Biological Resources Division server, and not indirectly through other sources which may have changed the data in some way.