This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.

# CDED

Standard format for the distribution of terrain elevation data for the United States.
Canadian Centre for Topographic Information (CTI) standard.
ASCII format.
Typically distributed as a ZIP compressed file.
The .dem file extension is often omitted.
Stores elevation data as a 1201×1201 raster.
CDED is available in 1:50,000 and 1:250,000 scales.
The longitudinal grid spacing varies with the latitude of the geographic area.
1:50,000 CDED uses a grid spacing of 0.75×0.75 arc second, 0.75×1.5 arc second, or 0.75×3 arc second.
1:250,000 CDED uses a grid spacing of 3×3 arc second, 3×6 arc second, or 3×12 arc second.
Elevations are expressed in meters relative to mean sea level.
• Import supports the CDED Level 1 standard.
• Import imports a CDED directory and renders it as a topographic map.
• Import imports from a CDED archive file.
• Import imports the specified element from CDED.
• Import imports multiple elements.
• When importing CDED topographic data, Mathematica reads information from multiple files contained in the CDED directory or archive file.
• See the reference pages for full general information on Import.
 "Elements" list of elements and options available in this file "Rules" full list of rules for each element and option "Options" list of rules for options, properties and settings
 "Data" array of terrain elevation values "Graphics" DEM file rendered as ReliefPlot "Image" raw DEM data as an image object "ReliefImage" DEM file rendered as ReliefImage
• Import by default uses for the CDED format.
 "Dimensions" size of the elevation data array "ElevationRange" range of elevation coordinates, given in meters "ElevationResolution" resolution of elevation values, given in meters "SpatialRange" range of geographic coordinates, given in decimal degrees "SpatialResolution" grid spacing in arc seconds
• Import gives the range of elevation values in units of meters.
• Import gives the bounding coordinates of the geographic region covered by the file as an expression of the form .
• Elements representing the geodetic datum and reference ellipsoid used in the file:
 "CoordinateSystem" name of the coordinate system used in the file "Datum" geodetic datum "SemimajorAxis" semimajor axis of the reference ellipsoid in meters "SemiminorAxis" semiminor axis of the reference ellipsoid in meters "InverseFlattening" inverse flattening of the ellipsoid "LinearUnits" coordinate system units
• Elements specifying the cartographic projection and its parameters:
 "Projection" projection name and parameters "Centering" latitude and longitude defining the origin of the projection "StandardParallels" standard parallels "CentralScaleFactor" scale factor at the central meridian or center of projection "GridOrigin" grid coordinates of the central parallel and meridian "ProjectionName" Mathematica standard name of the projection used "ReferenceModel" what reference sphere or ellipsoid to use
• Accessing low-level meta-information from the file:
 "CoordinateSystemInformation" raw parameters of the coordinate system as stored in the file
• See the reference page for GeoProjectionData for full information on cartographic projections.
 BoxRatios Automatic effective 3D bounding box ratios ColorFunction how to determine the color of surfaces DataRange Automatic the range of latitude and longitude values to assume for the data DataReversed False whether to reverse the order of rows ImageSize Automatic the overall size of the image LightingAngle Automatic the effective angle from which simulated illumination is taken to come