Adigital elevation model (DEM) ordigital surface model (DSM) is a3D computer graphics representation ofelevation data to representterrain or overlaying objects, commonly of aplanet,moon, orasteroid. A "global DEM" refers to adiscrete global grid. DEMs are used often ingeographic information systems (GIS), and are the most common basis for digitally producedrelief maps. Adigital terrain model (DTM) represents specifically the ground surface while DEM and DSM may represent tree topcanopy orbuilding roofs.

While a DSM may be useful forlandscape modeling,city modeling and visualization applications, a DTM is often required for flood or drainage modeling,land-use studies,^[1] geological applications, and other applications,^[2] and inplanetary science.

There is no universal usage of the termsdigital elevation model (DEM),digital terrain model (DTM) anddigital surface model (DSM) in scientific literature. In most cases the termdigital surface model represents the earth's surface and includes all objects on it. In contrast to a DSM, thedigital terrain model (DTM) represents the bare ground surface without any objects like plants and buildings (see the figure on the right).^[3][4]

DEM is often used as a generic term for DSMs and DTMs,^[5] only representing height information without any further definition about the surface.^[6] Other definitions equalise the terms DEM and DTM,^[7] equalise the terms DEM and DSM,^[8] define the DEM as a subset of the DTM, which also represents other morphological elements,^[9] or define a DEM as a rectangulargrid and a DTM as a three-dimensional model (TIN).^[10] Most of the data providers (USGS,ERSDAC,CGIAR,Spot Image) use the term DEM as a generic term for DSMs and DTMs. Some datasets such asSRTM or theASTER GDEM are originally DSMs, although in forested areas, SRTM reaches into the tree canopy giving readings somewhere between a DSM and a DTM). DTMs are created from high resolution DSM datasets using complex algorithms to filter out buildings and other objects, a process known as "bare-earth extraction".^[11][12]In the following, the term DEM is used as a generic term for DSMs and DTMs.

A DEM can be represented as araster (a grid of squares, also known as aheightmap when representing elevation) or as a vector-basedtriangular irregular network (TIN).^[13] The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is referred to as a secondary (computed) DEM.^[14] The DEM could be acquired through techniques such asphotogrammetry,lidar,IfSAR orInSAR,land surveying, etc. (Li et al. 2005).

DEMs are commonly built using data collected using remote sensing techniques, but they may also be built from land surveying.

The digital elevation model itself consists of a matrix of numbers, but the data from a DEM is often rendered in visual form to make it understandable to humans. This visualization may be in the form of a contouredtopographic map, or could use shading andfalse color assignment (or "pseudo-color") to render elevations as colors (for example, using green for the lowest elevations, shading to red, with white for the highest elevation.).

Visualizations are sometimes also done as oblique views, reconstructing a synthetic visual image of the terrain as it would appear looking down at an angle. In these oblique visualizations, elevations are sometimes scaled using "vertical exaggeration" in order to make subtle elevation differences more noticeable.^[15] Some scientists,^[16][17] however, object to vertical exaggeration as misleading the viewer about the true landscape.

Mappers may prepare digital elevation models in a number of ways, but they frequently useremote sensing rather than directsurvey data.

Older methods of generating DEMs often involveinterpolating digital contour maps that may have been produced by direct survey of the land surface. This method is still used inmountain areas, whereinterferometry is not always satisfactory. Note thatcontour line data or any other sampled elevation datasets (by GPS or ground survey) are not DEMs, but may be considered digital terrain models. A DEM implies that elevation is available continuously at each location in the study area.

One powerful technique for generating digital elevation models isinterferometric synthetic aperture radar where two passes of a radar satellite (such asRADARSAT-1 orTerraSAR-X orCosmo SkyMed), or a single pass if the satellite is equipped with two antennas (like theSRTM instrumentation), collect sufficient data to generate a digital elevation map tens of kilometers on a side with a resolution of around ten meters.^[18] Other kinds ofstereoscopic pairs can be employed using thedigital image correlation method, where two optical images are acquired with different angles taken from the same pass of an airplane or anEarth Observation Satellite (such as the HRS instrument ofSPOT5 or theVNIR band ofASTER).^[19]

TheSPOT 1 satellite (1986) provided the first usable elevation data for a sizeable portion of the planet's landmass, using two-pass stereoscopic correlation. Later, further data were provided by theEuropean Remote-Sensing Satellite (ERS, 1991) using the same method, theShuttle Radar Topography Mission (SRTM, 2000) using single-pass SAR and theAdvanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER, 2000) instrumentation on theTerra satellite using double-pass stereo pairs.^[19]

The HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs.

A tool of increasing value inplanetary science has been use of orbital altimetry used to make digital elevation map of planets. A primary tool for this islaser altimetry but radar altimetry is also used.^[20] Planetary digital elevation maps made using laser altimetry include theMars Orbiter Laser Altimeter (MOLA) mapping of Mars,^[21] theLunar Orbital Laser Altimeter (LOLA)^[22] and Lunar Altimeter (LALT) mapping of the Moon, and the Mercury Laser Altimeter (MLA) mapping of Mercury.^[23] In planetary mapping, each planetary body has a unique reference surface.^[24]New Horizons' Long Range Reconnaissance Imager used stereo photogrammetry to produce partial surface elevation maps ofPluto and486958 Arrokoth.^[25][26]

• Lidar^[27]
• Radar
• Stereo photogrammetry fromaerial surveys
  • Structure from motion / Multi-view stereo applied to aerial photography^[28]
• Block adjustment from optical satellite imagery
• Interferometry from radar data
• Real Time KinematicGPS
• Topographic maps
• Theodolite ortotal station
• Doppler radar
• Focus variation
• Inertial surveys
• Surveying and mappingdrones
• Range imaging

The quality of a DEM is a measure of how accurate elevation is at each pixel (absolute accuracy) and how accurately is the morphology presented (relative accuracy). Quality assessment of DEM can be performed by comparison of DEMs from different sources.^[29] Several factors play an important role for quality of DEM-derived products:

• terrain roughness;
• sampling density (elevation data collection method);
• grid resolution orpixel size;
• interpolation algorithm;
• vertical resolution;
• terrain analysis algorithm;
• Reference 3D products include quality masks that give information on the coastline, lake, snow, clouds, correlation etc.

Common uses of DEMs include:

• Extracting terrain parameters forgeomorphology
• Modelingwater flow forhydrology or mass movement (for exampleavalanches andlandslides)
• Modeling soils wetness with Cartographic Depth to Water Indexes (DTW-index)^[27]
• Creation of relief maps
• Rendering of3D visualizations.
• 3D flight planning andTERCOM
• Creation of physical models (includingraised relief maps and 3D printed terrain models)^[30]
• Rectification ofaerial photography orsatellite imagery
• Reduction (terrain correction) ofgravity measurements (gravimetry,physical geodesy)
• Terrain analysis ingeomorphology andphysical geography
• Geographic information systems (GIS)
• Engineering andinfrastructure design
• Satellite navigation (for exampleGPS andGLONASS)
• Line-of-sight analysis
• Base mapping
• Flight simulation
• Train simulation
• Precision farming andforestry^[31]
• Surface analysis
• Intelligent transportation systems (ITS)
• Auto safety /advanced driver-assistance systems (ADAS)
• Archaeology

Released at the beginning of 2022,FABDEM offers a bare earth simulation of the Earth's surface at 30 arc-second resolution. Adapted from GLO-30, the data removes all forests and buildings. The data is free to download non-commercially and through thedeveloper's website at a cost commercially.

An alternative free global DEM is calledGTOPO30 (30arcsecondresolution, c. 1 km along the equator) is available, but its quality is variable and in some areas it is very poor. A much higher quality DEM from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument of theTerra satellite is also freely available for 99% of the globe, and represents elevation at 30meter resolution. A similarly high resolution was previously only available for theUnited States territory under the Shuttle Radar Topography Mission (SRTM) data, while most of the rest of the planet was only covered in a 3 arc-second resolution (around 90 meters along the equator). SRTM does not cover the polar regions and has mountain and desert no data (void) areas. SRTM data, being derived from radar, represents the elevation of the first-reflected surface—quite often tree tops. So, the data are not necessarily representative of the ground surface, but the top of whatever is first encountered by the radar.

Submarine elevation (known asbathymetry) data is generated using ship-mounteddepth soundings. When land topography and bathymetry is combined, a trulyglobal relief model is obtained. The SRTM30Plus dataset (used inNASA World Wind) attempts to combine GTOPO30, SRTM and bathymetric data to produce a truly global elevation model.^[32] The Earth2014 global topography and relief model^[33] provides layered topography grids at 1 arc-minute resolution. Other than SRTM30plus, Earth2014 provides information on ice-sheet heights and bedrock (that is, topography below the ice) over Antarctica and Greenland. Another global model is Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) with 7.5 arc second resolution. It is based on SRTM data and combines other data outside SRTM coverage. A novel global DEM of postings lower than 12 m and a height accuracy of less than 2 m is expected from theTanDEM-X satellite mission which started in July 2010.

The most common grid (raster) spacing is between 50 and 500 meters. In gravimetry e.g., the primary grid may be 50 m, but is switched to 100 or 500 meters in distances of about 5 or 10 kilometers.

Since 2002, the HRS instrument on SPOT 5 has acquired over 100 million square kilometers of stereo pairs used to produce a DTED2 format DEM (with a 30-meter posting) DEM format DTED2 over 50 million km².^[34] The radar satelliteRADARSAT-2 has been used byMacDonald, Dettwiler and Associates Ltd. to provide DEMs for commercial and military customers.^[35]

In 2014, acquisitions from radar satellites TerraSAR-X and TanDEM-X will be available in the form of a uniform global coverage with a resolution of 12 meters.^[36]

ALOS provides since 2016 a global 1-arc second DSM free of charge,^[37] and a commercial 5 meter DSM/DTM.^[38]

Many national mapping agencies produce their own DEMs, often of a higher resolution and quality, but frequently these have to be purchased, and the cost is usually prohibitive to all except public authorities and large corporations. DEMs are often a product ofnational lidar dataset programs.

Free DEMs are also available forMars: the MEGDR, or Mission Experiment Gridded Data Record, from theMars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA) instrument; and NASA's Mars Digital Terrain Model (DTM).^[39]

OpenTopography^[40] is a web based community resource for access to high-resolution, Earth science-oriented, topography data (lidar and DEM data), and processing tools running on commodity and high performance compute system along with educational resources.^[41] OpenTopography is based at the San Diego Supercomputer Center^[42] at the University of California San Diego and is operated in collaboration with colleagues in the School of Earth and Space Exploration at Arizona State University and UNAVCO.^[43] Core operational support for OpenTopography comes from the National Science Foundation, Division of Earth Sciences.

The OpenDemSearcher is a Mapclient with a visualization of regions with free available middle and high resolution DEMs.^[44]

• Ground slope andaspect (groundspatial gradient)
• Digital outcrop model
• Global Relief Model
• Physical terrain model
• Terrain cartography
• Terrain rendering

• Bathymetric Attributed Grid (BAG)
• DTED
• DIMAP Sentinel 1 ESA data base
• SDTS DEM
• USGS DEM

• Wilson, J.P.; Gallant, J.C. (2000)."Chapter 1"(PDF). In Wilson, J.P.; Gallant, J.C. (eds.).Terrain Analysis: Principles and Applications. New York: Wiley. pp. 1–27.ISBN 978-0-471-32188-0. Retrieved2007-02-16.
• Hirt, C.; Filmer, M.S.; Featherstone, W.E. (2010)."Comparison and validation of recent freely-available ASTER-GDEM ver1, SRTM ver4.1 and GEODATA DEM-9S ver3 digital elevation models over Australia".Australian Journal of Earth Sciences.57 (3):337–347.Bibcode:2010AuJES..57..337H.doi:10.1080/08120091003677553.hdl:20.500.11937/43846.S2CID 140651372. RetrievedMay 5, 2012.
• Rexer, M.; Hirt, C. (2014)."Comparison of free high-resolution digital elevation data sets (ASTER GDEM2, SRTM v2.1/v4.1) and validation against accurate heights from the Australian National Gravity Database"(PDF).Australian Journal of Earth Sciences.61 (2):213–226.Bibcode:2014AuJES..61..213R.doi:10.1080/08120099.2014.884983.hdl:20.500.11937/38264.S2CID 3783826. Archived fromthe original(PDF) on June 7, 2016. RetrievedApril 24, 2014.

• DEM Quality Comparison
• Terrainmap.com
• Maps-for-free.com
• Geo-Spatial Data AcquisitionArchived 2013-08-22 at theWayback Machine
• Elevation Mapper, Create geo-referenced elevation maps

Data products

• Satellite Geodesy byScripps Institution of Oceanography
• Shuttle Radar Topography Mission by NASA/JPL
• Global 30 Arc-Second Elevation (GTOPO30) by the U.S. Geological Survey
• Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) by the U.S. Geological Survey
• Earth2014 byTechnische Universität München
• Sonny's LiDAR Digital Terrain Models of Europe