The National Elevation Dataset (NED) consists of high precision ground surface elevation data for the United States. It is maintained by the USGS and all the data is in the public domain.
Contents
Formats
Data is available in a few popular formats such as ESRI ArcGRID, GeoTIFF, BIL, GridFloat, and a few others.
Precision
Depending on area location, the datasets are provided with 1/9 (about 3 meters), 1/3 (about 10 m) and 1-arcsecond (about 30 m) precision.
References
National Elevation Dataset Wikipedia(Text) CC BY-SA