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D Back to Index Datum 1) Point, line or surface used as a reference for a measurement of another quantity. Point, line, or surface used as a reference (i.e., surveying, mapping, or geology). 2) Combination of parameters and control points used to accurately define the three dimensional shape of the Earth (spheroid). For example, the North American Datum for 1983 (NAD83) is the basis for map projections and coordinates within the United States and throughout North America. Digital Elevation Model Digital cartographic representation of a terrain surface or a subsurface feature as defined by a series of three-dimensional coordinate values. A digital representation of a continuous variable over a two dimensional surface by a regular array of Z values referenced to a common datum. DIME File Acronym for Dual Independent Map Encoding, a data format used by the U.S. Census Bureau to encode street network and related data for the 1980 Census. See TIGER for details. DTM Acronym for Digital Terrain Model, a representation of terrain relief in a computer readable format. Also referred to as a Digital Elevation Model. DXF Acronym for Data Exchange Format, a standard spatial data exchange format for CAD systems. DXF files contain ASCII or binary (DXB) records each of which describes a vector complete enough so that it can be converted into a spatial feature by any spatial database management product able to process these files. |
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