Digital Preservation Home | Digital Formats Home    

 Sustainability of Digital Formats: Planning for Library of Congress Collections
Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact
Format Description Categories >> Browse Alphabetical List

Digital Elevation Model (DEM) Format

>> Back
Table of Contents
Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name USGS Digital Elevation Model (DEM) Format, 1998
Description

A digital elevation model (DEM) represents terrain elevations for ground positions at regularly spaced horizontal intervals. The USGS "native" DEM format was developed specifically for this category of data and dates from 1992. A DEM dataset is a single file comprising 1024-byte ASCII-encoded (text) blocks that fall into three record categories called A, B, and C. There is no cross-platform ambiguity since line ending control codes are not used, and all data, including numbers, is represented in readable text form. A raster file format, DEM files usually contain terrain elevations, but the file format can be used for representing any surface. The format, allows internal documentation of coordinate system, date of publication, etc. These values are referenced horizontally, either to a Universal Transverse Mercator (UTM) projection or to a geographic coordinate system

The A record contains information defining the general characteristics of the DEM, including its name, boundaries, units of measurement, minimum and maximum elevations, number of B records, and projection parameters. Each B record consists of an elevation profile with associated header information, and the optional C record contains accuracy data. Each file contains a single A record and may contain a single C record, while there is a separate B record for each elevation profile.
Production phase DEM is a middle-state format used in the generation of three-dimensional graphics displaying terrain slope, aspect (direction of slope), and terrain profiles between selected points.

Local use Explanation of format description terms

LC experience or existing holdings The Library of Congress has a small number of DEM files in its collections.
LC preference See the Recommended Formats Statement for the Library of Congress format preferences for GIS, Geospatial and Non-GIS Cartographic data.

Sustainability factors Explanation of format description terms

Disclosure Openly published specification by United States Geological Survey (USGS). Standards for Digital Elevation Models (link via Internet Archive) specifies the collection, processing, and quality control of digital elevation model (DEM) data intended for entry into the National Digital Cartographic Data Base (NDCDB).
    Documentation Published by USGS at Digital Elevation Model Standards. "Standards for Digital Elevation Models" was published in 1997/8 as four documents: an introduction; Part 1: General; Part 2: Specifications