Terrain Data Download and Usage Guide

Terrain / elevation data describes the elevation form of the Earth's surface. It is usually expressed in meters together with horizontal coordinates, such as longitude/latitude or projected coordinates.

Concepts

• DEM (Digital Elevation Model): a general raster elevation model; depending on context, it may or may not distinguish terrain from surface objects.
• DTM (Digital Terrain Model): bare-earth elevation, with tree canopy and buildings removed.
• DSM (Digital Surface Model): surface elevation, including the highest surfaces such as tree canopy and buildings.

Data forms and formats

• Raster: the most common form, including GeoTIFF, Cloud-Optimized GeoTIFF, and BIL; pixel value = elevation.
• Point cloud: LAS/LAZ data from LiDAR or photogrammetry; can be used to derive DSM/DTM.
• Contours / TIN: vector contours or triangulated irregular networks for cartography or local modeling.

Typical sources

• Satellite / radar: SRTM, NASADEM, ASTER GDEM, ALOS AW3D, Copernicus DEM (GLO-30/90), and partly public TanDEM-X.
• Aerial survey / UAV photogrammetry (SfM): generates dense point clouds and DSM/DTM.
• Airborne / terrestrial LiDAR: high accuracy and high resolution, commonly used in urban and engineering applications.
• Bathymetry: GEBCO, EMODnet, and national hydrographic surveys; often merged with land DEMs into integrated land-and-sea terrain products such as ETOPO.

China Terrain Data

Introduction

A DEM represents ground relief using elevation values at regular grid points.

DEM data can be used to extract many terrain and geomorphology derivatives, including slope, aspect, drainage networks, 3D models, visibility analysis, and mobile-phone base-station analysis. DEMs are also used for quantitative analysis of terrain characteristics and to support planning and construction.

DEM product introduction from the National Geographic Information Resource Catalog Service System

The source lists typical DEM-related uses:

• Slope: Slope describes the steepness of a surface unit. Slope values can be used to classify landforms, such as plains, hills, and mountains.
• Aspect: Aspect is the direction of the projection of a slope normal on the horizontal plane; more simply, it is the downslope direction. Aspect can support analysis of shaded and sunny slopes, crop and vegetation light preferences, crop zoning, and selecting suitable slopes for returning farmland to forest.
• Site-selection planning analysis: By combining slope, aspect, and basic geographic information layers, overlay analysis can be applied in different industries. For example, urban construction usually needs flatter terrain.
• Hydrological analysis: DEMs can be used with fill-and-cut calculations to extract river networks and delineate watersheds.
• Viewshed analysis: DEM-based viewshed analysis divides the landscape into visible and invisible areas because terrain can block line of sight.

Main data products:

• 1:1,000,000 scale, corresponding to 400 m grid spacing.
• 1:250,000 scale, corresponding to 100 m grid spacing.
• 1:50,000 scale, corresponding to 25 m and 10 m grid spacing.

Download

After opening the page above, the right side lists digital elevation model data at different map scales. At present, however, the data is temporarily unavailable for download.

Coordinate System and Vertical Datum

This terrain data uses the China Geodetic Coordinate System 2000 and the 1985 National Height Datum.

The Yellow Sea height system and the 1985 National Height Datum: In 1956, China defined the long-term mean sea level of the Yellow Sea at Qingdao as the unified datum, called the 1956 Yellow Sea Height System. It was China's first national height system and ended the previous coexistence of many height systems. Because the Qingdao tide-gauge data series used for that datum (1950-1956) was short, China's surveying and mapping authority recalculated the Yellow Sea mean sea level using Qingdao tide observations from 1952 to 1979. This became the 1985 National Height Datum. Precise leveling was used at the national leveling origin in Qingdao, establishing the relationship: 1985 National Height Datum elevation = 1956 Yellow Sea elevation - 0.029 m. The 1985 datum was adopted in May 1987, and the 1956 Yellow Sea system was abolished. The 1956 leveling origin elevation was 72.289 m, and the 1985 leveling origin elevation is 72.260 m. Conventionally, the new datum is said to be 0.029 m lower than the old one. Source: National height system description

The 1985 National Height Datum is China's statutory national unified height system, based on the mean sea surface of the Yellow Sea and used as the standard for measuring ground elevation nationwide. Key points:

1. Definition and concepts

• Datum surface: the Yellow Sea mean sea level calculated from 28 years of Qingdao tide-gauge data from 1952 to 1979.
• Leveling origin: the national leveling origin of the People's Republic of China at Guanxiang Mountain, Qingdao, with an elevation of 72.260 m above the 1985 datum.

2. Technical principle

• Data improvement: compared with the 1956 Yellow Sea system, which used only 1950-1956 data, the 1985 datum uses a longer tide record and sliding-average calculations to reduce short-term sea-level fluctuation error.
• Conversion: 1985 datum elevation = 1956 Yellow Sea elevation - 0.029 m. For example, a point at 100 m in the 1956 system is 99.971 m in the 1985 system.

3. History

• Replacement of the old system: the 1985 datum was officially adopted in May 1987 with State Council approval, replacing the 1956 Yellow Sea Height System.
• Naming significance: although still based on the Yellow Sea, the name emphasizes national authority and avoids confusion with local height systems.

4. Applications

• Engineering and surveying: widely used in topographic mapping, construction projects such as bridges and dams, airport obstacle-control surfaces, and related fields.
• Relationship to other systems: Wusong elevation = 1956 Yellow Sea elevation + 1.688 m; Pearl River elevation = 1956 Yellow Sea elevation - 0.586 m. Unified conversions are required for compatibility.

5. Current status

As China's only statutory national height datum, it must be used in national surveying projects, map production, and land planning. Its parameters are governed by Specifications for the basic techniques of national geodesy (GB 22021-2008).

Global Terrain Datasets

Global terrain data digitally describes elevation for the whole Earth, either land-only or integrated land-and-sea. It is usually released as regular grids (raster DEM/DSM/DTM) or vector contour surfaces, representing the elevation or water depth at a location and supporting derivatives such as slope, aspect, viewshed, and hillshade.

Concept	Meaning
DEM (Digital Elevation Model)	General elevation raster; may include vegetation and buildings depending on source.
DSM (Digital Surface Model)	Surface model that keeps trees, buildings, ice sheets, and other surface objects.
DTM / Bare-earth	Bare-earth model with non-terrain objects removed; suitable for hydrology, flood, and geomorphology analysis.
Bathymetry	Seafloor depth, usually negative elevation; can be merged with land DEMs into land-and-sea grids.

Note: terrain data should be distinguished from land cover data.

Main data sources:

Method	Representative Datasets	Resolution	Characteristics
Synthetic Aperture Radar (SAR) interferometry	SRTM 1″/3″, TanDEM-X 12 m/90 m	12-90 m	Works under clouds and rain; partially penetrates vegetation.
Optical stereo photogrammetry	ASTER GDEM, ALOS AW3D30	30 m	Covers 83°N-83°S; cloud/snow areas may have gaps.
Optical-laser fusion + post-processing	Copernicus DEM GLO-30/90, FABDEM	30-90 m	Among the highest-quality public global products; FABDEM removes vegetation/buildings.
Laser altimetry / ice-penetrating radar	ICESat-2 correction, BedMachine	Regional 2-15 m	Improves polar and ice-sheet areas.
Multibeam and gravity-derived bathymetry	GEBCO, SRTM15+	15″ (~450 m)	Seafloor relief, merged with land DEMs.
Crowdsourcing / map fusion (OSM)	MERIT DEM, EarthEnv-DEM90	90 m	Multi-source fusion and error correction; hydrologically consistent versions exist.

Available Datasets

Dataset	Spatial Resolution at Equator	Type	Coverage	Latest Version	License and Access
Copernicus DEM GLO-30 / GLO-90	30 m / 90 m	DSM	Global land, including polar regions; 30 m is not fully public in some countries	DGED 2023_1	Free registration (Copernicus Data Space Ecosystem, portal.opentopography.org)
FABDEM	30 m	DTM, trees/buildings removed	Global land	2022+	Free academic version / commercial FABDEM+ (fathom.global)
ALOS World 3D-30 m (AW3D30)	30 m	DSM	Global land, with gaps in cloudy/snowy areas	v3.2 (2023)	Public and free (eorc.jaxa.jp)
ASTER GDEM v3	30 m	DSM	83°N-83°S, about 99% of land	2019	Public and free (asterweb.jpl.nasa.gov)
TanDEM-X	12 m commercial / 90 m public	DSM	Global land	90 m version 2023	90 m free, 12 m licensed (geoservice.dlr.de)
NASADEM / SRTM V3	30 m (1″) / 90 m (3″)	DSM	60°N-56°S, about 80% of land	2020	Public and free (portal.opentopography.org, USGS)
MERIT DEM	90 m	DTM, error/tree-height corrected	90°N-60°S	2019	Free for research (Global Hydrology Group)
EarthEnv-DEM90	90 m	DTM, smoothed fusion	90°N-60°S	2014	Public and free (earthenv.org)
IC2-GDEM	30 m	DTM, ASTER + ICESat-2 correction	83°N-83°S	2025 paper release	Research access (essd.copernicus.org)
GMTED2010	250 m / 7.5″	Multi-scale statistics	Global land	2010	Public and free (USGS)
GTOPO30	1 km	DEM	Global land	1996	Public and free (USGS)
GEBCO	15″, about 450 m	Land + seabed	Global land and ocean	2023	Public and free (GEBCO)

* DSM includes vegetation and buildings. DTM / bare-earth removes trees and buildings and is more suitable for hydrology, flood, and drainage-network simulation.

Selection and Usage Tips

1. First choice at 30 m: Copernicus GLO-30 currently has strong overall accuracy and consistency with a low download threshold. If bare-earth terrain is needed, use FABDEM, which removes building and canopy errors based on GLO-30. ALOS AW3D30 is a good alternative, especially where it complements ASTER in cloudy or snowy areas. IC2-GDEM improves high-latitude mountains but is still mainly a research release.
2. 90 m products: Copernicus GLO-90 and TanDEM-X 90 m are generally better than traditional SRTM in high-latitude and desert areas. MERIT DEM and EarthEnv-DEM90 include systematic error correction and are useful for large-basin hydrology or ecological modeling.
3. Integrated land-and-sea terrain: If analysis includes seafloor terrain, such as global visualization or sea-level-rise scenarios, use GEBCO 15″ global grids for consistent land-and-sea coverage.
4. Polar or high-precision needs: Polar regions can use TanDEM-X 12 m commercially or regional ArcticDEM/REMA 2 m. For ice-sheet thickness and bedrock, use BedMachine datasets for Greenland or Antarctica.
5. Data fusion and error control: Different DEMs may use different vertical references, such as ellipsoid heights versus EGM96 geoid heights, different acquisition periods, and DSM/DTM definitions. Before mosaicking datasets, unify the vertical datum and apply smoothing or bias correction. For large-scale hydrological or flood simulation, use hydrologically corrected products such as MERIT Hydro or FABDEM to reduce false drainage breaks and artificial depressions.

GEBCO Global Land-and-Sea Gridded Terrain Model

What Is GEBCO?

GEBCO (General Bathymetric Chart of the Oceans) is a century-scale project jointly led by the International Hydrographic Organization (IHO) and the Intergovernmental Oceanographic Commission (IOC) of UNESCO. Its goal is to complete high-precision global seafloor mapping by 2030 through the Seabed 2030 initiative. GEBCO's core product is an annually updated global land-and-sea gridded terrain model (GEBCO Grid), released free to the public for research, engineering, mapping, education, and other uses. GEBCO

Latest Versions

Version	Release Date	Spatial Resolution	Data Volume	Highlights
GEBCO_2025 Grid	2025-06-06	15″, about 500 m	3.7 x 10^9 pixels	Uses SRTM15+ v2.7 as the land and 50°S-60°N ocean base; includes latest multibeam bathymetry from four Seabed 2030 regional centers; 27.3% of the seafloor has modern bathymetry.
GEBCO_2024 Grid	2024-07-24	15″	Same	Adds 4.34 x 10^6 km² of data; first release with Greenland and Antarctica sub-ice versions.
GEBCO_2023 Grid	2023-07-12	15″	Same	Continues integrating regional-center and crowdsourced bathymetry data.

Data Components

• Elevation Grid: values are in meters; positive values represent land elevation and negative values represent water depth.
• TID Grid: each raster cell has a Type Identifier showing the data source, such as multibeam, single-beam, satellite-guided reconstruction, or interpolation. GEBCO
• Sub-ice versions: separate grids are available for topography under the Greenland and Antarctic ice sheets.

Download and Format

Method	Content	Format
Global file	1 NetCDF / GeoTIFF / Esri ASCII file	Single file, about 7.5 GB
8 tiles	90° x 90° tiles	About 890 MB per file, 8 files total
Online clipping	Custom extent download	GeoTIFF / NetCDF / ASCII
Web services	WMS, WMTS, TileXYZ	Suitable for online basemaps

GeoTIFF is usually recommended. Use the GEBCO_2024 Grid download address.

License and Citation

• Free: available for commercial and academic use.

• Requirement: cite "© GEBCO Year" and include the DOI, such as GEBCO_2025 10.5285/37c52e96-24ea-67ce-e063-7086abc05f29. British Oceanographic Data Centre

• Disclaimer: GEBCO is not responsible for losses caused by data use.

• Detailed documentation for each year is available through the DOI links.

  • GEBCO_2024 Grid
  • GEBCO_2023 Grid
  • GEBCO_2022 Grid
  • GEBCO_2021 Grid
  • GEBCO_2020 Grid
  • GEBCO 2019 Grid

Using the Data

After downloading GeoTIFF data, upload it to the cloud resource manager, or directly use the public-space precached data.

For this dataset, use standard global terrain coloring.

Zone	Class (m)	RGB	Description
Ultra-deep trench	≤ -8000	0, 0, 50	World's deepest trenches, such as the Mariana Trench
Deep ocean basin	-8000 to -6000	0, 40, 130	Deep ocean plain and basin
Abyssal plain	-6000 to -4000	0, 80, 200	Abyssal plain and ridge foot slopes
Oceanic slope	-4000 to -2000	0, 120, 240	Continental slope / mid-ocean ridge slopes
Outer continental shelf	-2000 to -200	70, 170, 255	Shallow-sea to slope transition
Continental shelf and tidal flats	-200 to 0	172, 220, 255	Nearshore shallows and deltas
Coastline / lowland	0 to 200	0, 120, 0	Low-elevation coastal plains and estuaries
Low hills	200 to 1000	80, 160, 0	Rolling hills and low mountains
Middle mountains	1000 to 2000	172, 172, 0	Plateau margins and pastoral highlands
Plateau	2000 to 3000	200, 150, 0	Inland plateaus and tablelands
Low mountain ridges	3000 to 4000	210, 110, 35	Mountain ridges and exposed rock walls
High mountains	4000 to 5000	220, 170, 130	Alpine valleys and first snow/ice zones
Extremely high mountains	5000 to 6000	240, 220, 200	High-altitude glacier areas
Snow line	6000 to 8848	250, 250, 250	Perennial snow and ice caps
Highest peaks	≥ 8848	255, 255, 255	Everest and other extreme elevations

In iXGIS, you can use stretch coloring or classified coloring. Hillshade can also be enabled with classified coloring.

Simplified GEBCO Template

A simplified global land-and-sea terrain map can be made by reducing the original data by a factor of 10.

1. Load the simplified GEBCO global land-and-sea raster terrain model from the public space. The resolution is 45'.
2. Configure symbols and styles. You can use the global land-and-sea terrain colors listed above, with either stretch or classified symbols. The example uses stretch colors. If the project is created from the Global Terrain GEBCO template, the existing symbol settings can be reused.
3. Load the simplified global country distribution layer.
4. Enter map layout and add a north arrow, scale bar, and legend.
5. Select the map frame and set the map scale to 1:150,000,000 in map properties.

ASTER GDEM v3

On June 30, 2009, NASA and Japan's Ministry of Economy, Trade and Industry (METI) jointly released the ASTER GDEM (Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model), produced from detailed observations by NASA's Terra satellite. This global DEM uses 1.3 million stereo images collected by ASTER. ASTER mapping covers all land areas between 83°N and 83°S, about 99% of Earth's land surface. Before this, the most complete terrain data came from NASA's Shuttle Radar Topography Mission (SRTM), which mapped about 80% of Earth's land between 60°N and 57°S.

At one time, SRTM 90 m terrain data could be downloaded for free from the International Scientific Data Service Platform of the Computer Network Information Center, Chinese Academy of Sciences (http://srtm.datamirror.csdb.cn/). It is no longer available there.

Production Workflow

ASTER GDEM was produced by fully automated processing of 1.5 million archived ASTER scenes. This included 1,264,118 scene-based ASTER DEMs generated through stereo correlation, followed by cloud removal, removal of remaining anomalies, averaging to produce final pixel values, correction of remaining abnormal data, and tiling into 1° x 1° global ASTER GDEM files.

Data Access

ASTER GDEM data is currently available online for free. Users can download it from Japan's ERSDAC (Earth Remote Sensing Data Analysis Center) or NASA's LP DAAC (Land Processes Distributed Active Archive Center). Registration and data-request permissions are required before download.

Access from iXGIS

iXGIS has downloaded the data from the sources above and cached it in object storage. Users can download it directly from the Data Download tool in the toolbox. The download format is GeoTIFF.

iXGIS automatically merges and clips the data according to the specified extent.

Global data download is supported.

NASADEM / SRTM V3

NASADEM (NASA Digital Elevation Model) is a high-precision global digital elevation product developed by NASA from SRTM V3 (Shuttle Radar Topography Mission, Version 3) data. SRTM was acquired in 2000 by radar interferometry aboard the Space Shuttle Endeavour, covering most land areas between 60°N and 56°S, or more than 80% of global land.

NASADEM comprehensively reprocesses and enhances SRTM by combining multiple data sources, such as ASTER GDEM, ICESat, NED/3DEP, and GTOPO30, with improved processing algorithms to improve accuracy, completeness, and consistency.

Data Characteristics

• Coverage: global 60°N-56°S, covering most inhabited land areas.
• Spatial resolution: 1 arc-second (~30 m) global coverage for SRTM1; 3 arc-second (~90 m) global coverage for SRTM3 and some historical versions.
• Vertical accuracy: absolute vertical accuracy is about < 10 m, and relative accuracy is better than 5 m. NASADEM reprocessing further reduces errors.
• Projection and format: WGS84 ellipsoid, geographic coordinates EPSG:4326, GeoTIFF tiles of 1° x 1°.
• Processing improvements over SRTM V2 and CGIAR-CSI SRTM: NASA JPL's new algorithm fills voids in the original data; multiple elevation sources such as ASTER GDEM, NED/3DEP, and ICESat are fused for correction; global seamless coverage is improved; and outputs are better suited for integration with other NASA/USGS datasets such as Landsat and MODIS.

Access

• NASA Earthdata (LP DAAC): https://lpdaac.usgs.gov/
• USGS EarthExplorer: https://earthexplorer.usgs.gov/

AW3D30-DSM

AW3D30 is a global digital surface model (DSM) produced by the Japan Aerospace Exploration Agency (JAXA) from imagery acquired by PRISM (Panchromatic Remote-sensing Instrument for Stereo Mapping) aboard the Advanced Land Observing Satellite ALOS, also called DAICHI.

• Spatial resolution: about 30 m (1 arc-second grid).
• Coverage: global land areas; exact coverage depends on product version.
• License: the dataset can be used free of charge for commercial and non-commercial purposes, subject to the applicable terms of use.

Access

• Register on JAXA's EORC official website and download tile packages, usually provided as *.tar.gz files.
• Access and analyze it in Google Earth Engine, for example using ImageCollection "JAXA/ALOS/AW3D30/V4_1" and the DSM band for visualization or slope calculation.
• Data download
• After email registration, tiled files can be downloaded.

File Organization

AW3D30 data is organized as 1° x 1° longitude/latitude tiles. Main files include:

• DSM file: surface height (elevation), stored as 16-bit signed values.
• MSK file: 8-bit mask marking cloud, snow, seawater, low-quality areas, and similar conditions.
• STK file: indicates the number of scene stacks used to generate the DSM.
• QAI file: quality-assurance information describing product properties and data quality.
• HDR file: metadata file containing projection, data format, and related information.

Access from iXGIS

iXGIS has downloaded the data from the source above and cached it in object storage. Users can download it directly from the Data Download tool in the toolbox. The download format is GeoTIFF.

iXGIS automatically merges and clips the data according to the specified extent.

Global data download is supported.