DEM

The Digital Elevation Model (DEM) format is an open standard developed in 1992 by the U.S. Geological Survey (USGS) for representing terrain elevations for ground positions at regularly spaced horizontal intervals. A DEM dataset is a single file comprising 1024-byte ASCII-encoded (text) blocks that fall into three record categories: a single A-type record defining general characteristics for the dataset; a B-type record for each elevation profile (one-dimensional band of elevation values); and a single, optional C-type record with accuracy data.

DEM files have been produced by the U.S. Geological Survey (USGS) as part of the National Mapping Program in five different products based on 7.5-minute, 15-minute, 2-arc-second (also known as 30-minute), and 1-degree grids on the earth surface.

The DEM format was developed by USGS in 1992 and is used throughout the world. For USGS use, DEM has been superseded by the SDTS format but the DEM format remains popular because large numbers of legacy files exist nd are still of value, its structure is self-contained with a relatively simple field structure, and the format has broad, mature software support.