General Bathymetric Chart of the Oceans (GEBCO)
GEBCO_08 Grid
The GEBCO_08 Grid is a 30 arc-second grid of global elevations; it is a continuous terrain model for ocean and land.
The grid was generated by combining quality-controlled ship depth soundings with interpolation between sounding points guided by satellite-derived gravity data. The land data are largely taken from the Shuttle Radar Topography Mission (SRTM30) data set.
The grid is accompanied by a Source Identifier (SID) Grid. This data set identifies which grid cells in the GEBCO_08 Grid are based on bathymetric soundings or bathymetric depth values from grids and which cells contain predicted depth values.
Find out about
- Data set documentation and bug alerts
- Data set update history
- Source Identifier (SID) Grid
- Grid version numbering
- Grid export formats
- Grid display and data access software
Data set documentation and bug alerts
Users are referred to the 'Documentation for the GEBCO_08 Grid' 
(31 KB) for details on the data sources used in the development of the grid, and
are strongly advised to read it before making use of the data set.
This data set is currently a development product which will undergo periodic update. Although every effort has been made to reduce the number of errors in the data set, we expect that some grid artifacts will be found. See the errata pages for a list of reported bugs.
If you find any un-reported bugs in the grid please report them via e-mail (enquiries@bodc.ac.uk), including the problem location, and we will investigate.
Data set update history
| Version number | Update | Release date |
|---|---|---|
| 20100927 |
i) Bathymetric grids for the Black Sea region provided by Dr. John Hall, Geological Survey of Israel (retired), based on bathymetric soundings digitised from Russian hydrographic charts. ii) Bathymetric grids for the Caspian Sea region provided by Dr. John Hall, Geological Survey of Israel (retired), based on bathymetric soundings digitised from Russian hydrographic charts. iii) Bathymetric grid for the Weddell Sea provided by the Alfred Wegener Institute for Polar and Marine Research (AWI). The grid is based on the bathymetric Chart of the Weddell Sea (BCWS). |
2010-09-27 |
| 20091120 | Inclusion of version 2.23 of the International Bathymetric Chart of the Arctic Ocean (IBCAO) for the region 64N-90N; 180W-180E | 2009-11-24 |
Source Identifier (SID) Grid
The GEBCO_08 Grid is accompanied by a 'source identifier' or SID grid. This data set identifies which grid cells in the GEBCO_08 Grid are based on bathymetric soundings or bathymetric depth values from grids and which cells contain predicted depth values.
For future releases, it is planned that the SID grid will contain an identifier code which will identify the individual surveys used to generate the data set.
Grid version numbering
The gridded data are taken from version 20100927 of the GEBCO_08 Grid. The version number is taken from the release date of the data set, i.e. year, month, day.
Grid export formats
The gridded data are stored in a netCDF data file.
Within the GEBCO_08 Grid and GEBCO_08 SID Grid netCDF files, the grids are stored as one dimensional arrays of 2-byte signed integer values.
The complete data sets provide global coverages. Each data set consists of 21,600 rows x 43,200 columns, resulting in a total of 933,120,000 data points. The data start at the Northwest corner of the file, i.e. for the global file, position 89°59'45"N, 179°59'45"W, and are arranged in latitudinal bands of 360 degrees x 120 points/degree = 43,200 values. The data range eastward from 179°59'45"W to 179°59'45"E. Thus, the first band contains 43,200 values for 89°59'45"N, then followed by a band of 43,200 values at 89°59'15"N and so on at 30 arc-second latitude intervals down to 89°59'45"S.
The data values are pixel centred registered i.e. they refer to elevations at the centre of grid cells. For example, the data point at 179°59'45"W, 89°59'45"N represents the data value at the centre of a grid cell of dimension 30 arc-seconds of latitude and longitude centred on this position i.e. 179°59'30"W - 180°W; 89°59'30"N - 90°N.
The netCDF files are compatible with the Generic Mapping Tools (GMT) system.
Data coding
GEBCO_08 Grid
The data values within the GEBCO_08 Grid represent elevation in metres, with negative values for bathymetric depths and positive values for topographic heights.
GEBCO_08 SID Grid
The SID grid data values are coded as follows:
| SID file coding | Description |
|---|---|
| 0 | The grid value at this location has been developed from a database of ship-track soundings with interpolation between soundings guided by satellite-derived gravity data.
At this location in the grid, the data value has been interpolated. |
| 9999 | The grid value at this location has been developed from a database of ship-track soundings with interpolation between soundings guided by satellite-derived gravity data.
At this location, the grid cell has been constrained by a bathymetric sounding(s) data during the gridding process. |
| -8888 | The grid value at this location has a positive value (+ve), i.e. is coded as land. |
| 110 | The grid value at this location is taken from the Caspian Sea grid, (see Annex B.1). This grid has been generated from a data set of soundings using a kriging gridding algorithm.
SID grid cells which contain a sounding(s) from the Caspian Sea source data set are coded as ‘1100’. |
| 120 | The grid value at this location is taken from the Black Sea grid, (see Annex B.2). This grid has been generated from a data set of soundings using a kriging gridding algorithm.
SID grid cells which contain a sounding(s) from the Black Sea source data set are coded as ‘1200’. |
| 130 | The grid value at this location is taken from the Weddell Sea grid, (see Annex B.3). This grid has been generated from a data set of bathymetric contours based largely on multi-beam and single beam bathymetric surveys.
SID grid cells which contain trackline control from the Weddell Sea source data set are coded as ‘1300’. |
| 1000 | The grid value at this location is taken from version 2.23 of the International Bathymetric Chart of the Arctic Ocean (IBCAO), (see Annex A.1). |
| 1100 | The grid value at this location is taken from the Caspian Sea grid, (see Annex B.1). The grid cell at this location contains a sounding(s) from the Caspian Sea source data set.
For the Caspian Sea grid, cells which do not contain a sounding(s) are coded as ‘110’. |
| 1200 | The grid value at this location is taken from the Black Sea grid, (see Annex B.2). The grid cell at this location contains a sounding(s) from the Black Sea source data set.
For the Black Sea grid, cells which do not contain a sounding(s) are coded as ‘120’. |
| 1300 | The grid value at this location is taken from the Weddell Sea grid, (see Annex B.3). This grid has been generated from a data set of bathymetric contours based largely on multi-beam and single beam bathymetric surveys.
The grid cell at this location is ‘crossed’ by trackline control information, i.e. survey track or isolated sounding, from the Weddell Sea source data set. For the Weddell Sea grid, cells which do not contain trackline control are coded as ‘130’. |
Grid display and data access software
Interface software is available for displaying and accessing data from GEBCO's gridded bathymetric data sets in netCDF and also in simple ASCII formats, including one suitable for conversion to a raster file which can be used with ESRI arcGIS products. Please note that the software is designed for use with a complete, global GEBCO gridded data set file. The software will not work with subsets of the full data set(s).
Find out more about the GEBCO Grid display software
Related GEBCO pages at BODC |
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| GEBCO at BODC | Data set errata |
Related external links |
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| Official GEBCO web site | Shuttle Radar Topography Mission (SRTM30) |
| Generic Mapping Tools (GMT) | network Common Data Form (netCDF) |
| International Hydrographic Organization (IHO) | Intergovernmental Oceanographic Commission (IOC) |
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