What are the projection, horizontal and vertical datum, units, and cell size for NED?
The NED data are not projected, but are provided in geographic coordinates (latitude and longitude) in units of decimal degrees, horizontally referenced to the North American Datum of 1983. All elevation values are in units of meters typically referenced to the North American Vertical Datum of 1988, although the National Geodetic Vertical Datum of 1929 and local reference surfaces are used in some areas outside of the conterminous United States. Most areas within the NED are available at a cell spacing (resolution) of 1 arc-second (approx. 30 meters), and 1/3 arc-second (approx. 10 meters). Some areas from specific sources are also available at a cell spacing of 1/9 arc-second (approx. 3 meters). The bulk of Alaska is, at this writing, only available at a point spacing of 2 arc-seconds (approx. 60 meters).
