The following XML output stream is an example of the way extracted metadata is retrieved. The standard DEM consists of a regular array of elevations cast on a designated coordinate projection system. The DEM data are stored as a series of profiles in which the spacing of the elevations along and between each profile is in regular whole number intervals. The normal orientation of data is by columns and rows. Each column contains a series of elevations ordered from south to north with the order of the columns from west to east.
Coverage is for the United States.
The accuracy of a DEM is dependent upon the level of detail of the source and the grid spacing used to sample that source. The primary limiting factor for the level of detail of the source is the scale of the source materials. NMAS horizontal accuracy requires that at least percent of points tested are within inches of the true position. The primary reference from which degree DEM accuracy is derived is source-based, as a minimum, meeting NMAS for ,000 scale USGS topographic series maps. Wrappers Wrappers are used for providing structured query access to otherwise only browsable Web sources.