Elevation

There are a number of Mac software packages that will read elevation files. Five that came up in a quick Web search are: Cartographica uDig Grass GIS Quantum GIS Geospatial Data Abstraction Library The Geospatial Data Abstraction Library (GDAL) scripts...
Spot elevation data queries originate from the National Elevation Dataset (NED) of the U.S. Geological Survey (USGS). Elevation values are not official and do not represent precisely measured or surveyed values. Data are extracted from digital elevation...
All NED data are in the public domain and may be used without restriction. We do request that proper credit be given when used for redistribution, resale, presentation or publication. Please refer to Acknowledging or Crediting USGS as Information Source...
Yes. To maintain consistency, the NED data distributed from USGS are only produced on NAD83 with a geographic coordinate system. Users can project the NED data to a different datum or projection using most GIS software after downloading the data....
Elevations are centered to each pixel in raster datasets, which are used by most GIS applications.
There are frequently multiple sources of elevation data that cover a given location. Preference is given to that which is the most detailed and up-to-date, unless there are overriding quality concerns. An important qualification is that any candidate...
The Data Source Index map shows areas which have been updated for all resolutions of the NED and is viewable at the NED Data Source Index within The National Map Viewer. Spatial metadata shapefiles showing the updated areas for each resolution are also...
 DatasetMinimum Delivery PackagesFormatProjectionSize Estimates (Zipped) NED 2 Arc Second - AlaskaComplete DatasetArcGrid,Gridfloator .IMGGeographic4.0 Gbytes 4.0 Gbytes4.0 Gbytes NED 1 Arc SecondComplete DatasetArcGrid,Gridfloator .IMGGeographic84.0...
The NED is derived from diverse source data that are processed to a common coordinate system and unit of vertical measure. All NED elevation values are in meters. To convert the Z unit of downloaded NED data from meters to feet, use this formula:  feet...