For educational/demonstration purposes only. The Originator, Publisher and Distributor exclude any and all implied warranties and make no warranty or representation with respect to the data files or accompanying documentation, including quality, performance, merchantability or fitness for a particular purpose. These data files and documentation are provided 'as is' and the User assumes the entire risk as to their quality and performance
These data are not to be redistributed for commercial profit. Reproduction or redistribution of this digital data set without permission of the Originator/Publisher is expressly forbidden. The Originator and Publisher should be clearly cited in any product derived from this data. Any modifications to this data must be described in any digital or hardcopy product derived from this data.
Until an independent overall assessment of the accuracy of NED is completed, it is best to refer to published information on the accuracy of the source digital elevation models (DEM's) from which NED was assembled. The primary source data were the USGS 7.5-minute (30-meter or 10-meter resolution) DEM's. Gaps in the 7.5-minute DEM coverage were filled with data from USGS 30-minute (2-arc-second resolution) or 1-degree (3-arc-second resolution) DEM's. The USGS Data Users Guide 5 for DEM's (traditionally known as the "blue book"), last published in 1993, contains a general discussion of DEM accuracy and a brief description of the accuracy testing methodology.
The DEM data users guide also describes the classification levels of standard USGS DEM products. The level of a DEM is defined, in part, on the basis of its accuracy.