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A digital elevation model (DEM) is a gridded representation of the Earth’s surface height. In the USGS usage, a DEM shows the bare-earth topographic surface, with trees, buildings and other surface objects removed. The detail that decides whether your analysis is reproducible is which surface a given dataset actually models, which vertical datum its heights use, and when its source data were collected. This guide compares three widely used open sources (SRTM, USGS 3DEP and Copernicus DEM) and lists what to record when you cite or archive a DEM.
Short answer
A DEM is an elevation raster. Whether it includes vegetation and buildings depends on the product: USGS 3DEP DEMs are bare-earth, while the Copernicus DEM is explicitly a surface model that includes them. SRTM, 3DEP and Copernicus DEM are all openly available, but they differ in resolution, coverage, vertical datum and acquisition date, so a DEM should be cited and archived with those details.
Definition and scope
The USGS defines a DEM as a representation of the bare-ground (bare-earth) topographic surface of the Earth, excluding trees, buildings and any other surface objects. USGS DEMs were once derived mainly from topographic maps and are being replaced by high-resolution lidar DEMs and, in Alaska, by IfSAR-derived products. Terrain heights are stored on a regular grid, so each cell holds one elevation value and the cell size sets the horizontal resolution.
Terminology is not uniform across fields. Some GIS users call any elevation raster a DEM, while agencies use “DEM”, “digital surface model (DSM)” and “digital terrain model (DTM)” with different meanings. State which meaning your deliverable uses rather than assuming the reader shares it.
How DEMs are produced and used in practice
- Lidar. The USGS 1-meter DEM is a bare-earth DEM produced from lidar. The underlying lidar point clouds are distributed separately in LAZ format.
- IfSAR. In Alaska, USGS publishes a 5-meter DEM from interferometric synthetic aperture radar, distributed as GeoTIFF.
- Space-borne radar. SRTM collected radar data between 60°N and 56°S, covering more than 80 percent of land, during a Space Shuttle Endeavour flight on 11 to 22 February 2000. The Copernicus DEM is derived from TanDEM-X radar acquisitions made between 2011 and 2015, with older models filling gaps.
The common formats offered by these sources include GeoTIFF (3DEP 1-meter seamless, 5-meter Alaska IfSAR, SRTM) and DTED and BIL (SRTM).
DEM vs DSM vs DTM
Digital elevation model (DEM)
Under the USGS definition, bare earth only. In general GIS usage, sometimes any gridded elevation.
Digital surface model (DSM)
The Copernicus DEM documentation describes its product as a DSM that “represents the top-reflective surface of the Earth including buildings, infrastructure and vegetation.” Despite the name “Copernicus DEM”, it is therefore not a bare-earth model.
Digital terrain model (DTM)
Usage varies: some authors treat DTM as a synonym of a bare-earth DEM, others as bare earth plus additional features such as breaklines. Because no single international definition governs this, check the documentation of the specific dataset and record the surface type in your metadata.
Open DEM datasets compared
Each row below is taken from the provider’s own product page (read 7 November 2026).
| Dataset | Resolution | Coverage | Surface | Vertical datum / horizontal reference | Source data and date |
|---|---|---|---|---|---|
| SRTM 1 arc-second (USGS EROS) | About 30 m (tiles above 50°N/S sampled 2 by 1 arc-second) | Global between 60°N and 56°S, more than 80% of land | Radar-derived elevation; void-filled, though some tiles may still contain voids | EGM96, metres; WGS84 | Shuttle radar, 11-22 February 2000 |
| USGS 3DEP 1-meter | 1 m | Project-based, limited but expanding; seamless S1M tiles added as available (production began mid-2025) | Bare earth from lidar | Read from tile metadata | Lidar collected by project |
| USGS 3DEP 1/3 arc-second seamless | About 10 m | 48 conterminous states, Alaska, Hawaii and territories | Bare earth | Read from tile metadata | Vertical accuracy of about 0.82 m RMSE for the conterminous US (USGS, as of 2022) |
| USGS 3DEP 1 arc-second seamless | About 30 m | Conterminous US, Alaska, most of Canada and Mexico | Bare earth | Read from tile metadata | Not stated on the product page |
| Copernicus DEM GLO-30 / GLO-90 | 30 m / 90 m | Global, about 149 million km² | DSM: includes buildings, infrastructure and vegetation | EGM2008 (EPSG:3855), metres; WGS84 (EPSG:4326) | TanDEM-X, 2011-2015; absolute vertical accuracy under 4 m and horizontal under 6 m (90% confidence) |
Two comparisons follow from the table. First, SRTM (EGM96) and Copernicus (EGM2008) use different geoid models for heights, so mixing them without checking the datum can introduce an offset. Second, 3DEP and Copernicus describe different surfaces, so over forest or cities the same location will not give the same value. Their acquisition dates also differ by up to about 15 years, which matters wherever the terrain has changed.
What to record when you cite or archive a DEM
Elevation grids are a common input to hydrology, geomorphology and ecology work, and results depend on them. Descriptive metadata that travels with the derived data lets someone else repeat the analysis; see descriptive metadata for datasets. A practical checklist based on the facts above:
- Dataset name, provider and version or tile identifiers.
- Horizontal resolution and coverage used.
- Surface type as the provider defines it (bare earth or surface model).
- Vertical datum (for example EGM96 or EGM2008) and horizontal reference system.
- Acquisition period of the source data (for example 2000 for SRTM, 2011-2015 for Copernicus).
- Licence and required attribution. For Copernicus DEM GLO-30 and GLO-90, the provider states a free licence worldwide for registered users and gives the attribution notice “provided under COPERNICUS by the European Union and ESA; all rights reserved”.
- A persistent identifier where one exists, such as the Copernicus DEM DOI
10.5270/ESA-c5d3d65, in line with the data citation principle.
If you publish a derived DEM or terrain product, deposit it in a repository that gives it its own identifier; how to choose an open data repository covers the options, and USGS ScienceBase is one example of a repository for USGS-related data.
Common misunderstandings
- “A DEM always excludes vegetation.” That is the USGS definition, but the Copernicus DEM is a surface model that includes it.
- “The most recent-looking dataset is the most current.” Seamless products are compiled from source data of different dates; SRTM reflects February 2000 and Copernicus 2011-2015.
- “30 m means 30 m accuracy.” Resolution is the grid spacing. Accuracy is stated separately, for example under 4 m absolute vertical for Copernicus (90% linear error).
- “SRTM has no gaps.” It is void-filled worldwide, but some tiles may still have voids.
FAQ
Where can I download a free digital elevation model?
USGS offers 3DEP products (1 m, 1/3 and 1 arc-second, and 5 m in Alaska) and the SRTM 1 arc-second archive through its EROS and 3DEP services. The Copernicus DEM GLO-30 and GLO-90 are available from the Copernicus Data Space Ecosystem under a free licence for registered users. The OpenDEM site also lists free models, including SRTM.
What is an example of a digital elevation model?
The USGS 1/3 arc-second seamless DEM covering the conterminous United States, with a vertical accuracy of about 0.82 m RMSE, and the global 30 m Copernicus GLO-30 DEM are two examples with different surface definitions.
What are the types of digital elevation model?
By production method: lidar-derived, IfSAR-derived and satellite radar-derived (SRTM, TanDEM-X). By surface represented: bare-earth DEMs and surface models (DSMs); some authors add DTMs.
How is a DEM used in GIS?
A DEM is loaded as a raster layer, with the coordinate reference system and vertical datum matched to the other data in the project before terrain derivatives are computed.
What is the difference between a DTM and a DEM?
There is no single international standard. The USGS DEM is bare earth; some authors use DTM for the same thing, others for bare earth plus breaklines. Record the definition used.
Sources
- USGS, What is a digital elevation model (DEM)?, read 7 November 2026.
- USGS, About 3DEP products and services, read 7 November 2026.
- Copernicus Data Space Ecosystem, Copernicus DEM (COP-DEM) collection description, DOI 10.5270/ESA-c5d3d65, read 7 November 2026.
- USGS EROS Archive, Shuttle Radar Topography Mission (SRTM) 1 Arc-Second Global, read 7 November 2026.
- OpenDEM, Free Digital Elevation Models, read 7 November 2026.
