GEBCO grid formats
The General bathymetric Chart of the Oceans (GEBCO) develops global gridded bathymetric data sets. These grids are maintained and made available, on behalf of GEBCO, by BODC. GEBCO's gridded data sets consist of
- The GEBCO_2014 Grid — a global terrain model at 30-arc second intervals
- The GEBCO_2014 Source Identifier (SID) Grid — 'metadata' grid to accompany the GEBCO_2014 Grid
- The GEBCO One Minute Grid — a global terrain model at one arc-minute intervals
The GEBCO_2014 Grid and SID Grid are available to download for user-defined areas in netCDF; Esri ASCII raster or INT16 data GeoTiff formats. The GEBCO One Minute Grid is available in netCDF format only.
In netCDF format the grids are available as either two-dimensional (2D) or one-dimensional (1D) array grid files. The 2D array grids use the Climate and Forecast (CF) metadata conventions. You can download data for a user-defined area or the complete global grid. The 1D array grids are for use with GEBCO's Grid Display Software and GEBCO Digital Atlas (GDA) and so are only available as a global grid.
Find more about
- 2D netCDF data sets — consistent with the BODC Climate and Forecast (CF) netCDF format
- 1D netCDF data sets — for use with the GEBCO Digital Atlas and GEBCO Grid Display software packages
- Esri ASCII raster format
- External software packages
2D netCDF data sets
Each file consists of two sections
The CF header
The CF metadata header is split into a number of components, namely; dimensions, variables and global attributes. For more information please refer to the components of a BODC CF-compliant netCDF file. An illustration of the GEBCO_2014 CF header (59 KB) is available as an Adobe PDF file.
The data section
This section of the file contains the actual values for each dimension and variable. The data values represent elevation in metres, with negative values for bathymetric depths and positive values for topographic heights.
GEBCO_2014 Grid and GEBCO_2014 Source Identifier Grid
The complete data sets gives global coverage, spanning 90°N, 180°W to 90°S, 180°E on a 30 arc-second grid. Each grid consists of 21,600 rows x 43,200 columns, giving 933,120,000 data points. The data values are pixel centre registered i.e. they refer to elevations at the centre of grid cells.
GEBCO One Minute Grid
The complete data set gives global coverage, spanning 90°N, 180°W to 90°S 180°E on a one arc-minute grid. The grid consists of 10,801 rows x 21,601 columns giving a total of 233,312,401 points. The data values are grid line registered i.e. they refer to elevations centred on the intersection of the grid lines.
1D netCDF data sets
GEBCO's 1D grids are, primarily, for use with the GEBCO Digital Atlas and GEBCO Grid Display software packages. The data are stored as a 1D array of 2-byte signed integer values of elevation in metres, with negative values for bathymetric depths and positive values for topographic heights.
- GEBCO_2014 Grid and GEBCO_2014 Source Identifier Grid
Each grid consists of 21,600 rows x 43,200 columns, resulting in 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 centre registered i.e. they refer to elevations at the centre of grid cells.
- GEBCO One Minute Grid
The grid consists of 10,801 rows x 21,601 columns, resulting in a total of 233,312,401 points. The data start at position 90°N, 180°W and are arranged in latitudinal bands of 360 degrees x 60 points/degree + 1 = 21,601 values. The data range eastward from 180°W to 180°E. i.e. the 180° value is repeated. Thus, the first band contains 21,601 repeated values for 90°N, then followed by a band of 21,601 values at 89° 59'N and so on at one minute latitude intervals down to 90°S. The data values are grid line registered i.e. they refer to elevations centred on the intersection of the grid lines.
Esri ASCII raster format
This is an ASCII format developed for the export/exchange of Esri ARC/INFO rasters. The format consists of a header that gives the geographic extent and grid interval of the data set, followed by the actual grid cell data values.
The GeoTiff format contains georeferencing (geographic extent and projection) information embedded within a Tiff file. The GEBCO_2014 Grid and SID grids are made available as single-channel INT16 (two byte signed integer) data values for user-defined areas in GeoTiff format.
External software packages
GEBCO's grids can be used with a number of software packages and systems. The following are given as examples
Generic Mapping Tools (GMT)
Both of GEBCO's 1D and 2D netCDF format grids can be used directly with the GMT software system. GMT is an open source collection of around 65 tools for manipulating geographic and Cartesian data sets (including filtering, trend fitting, gridding, projecting, etc.) and producing image files from the data sets.
Esri ArcGIS Desktop software pages
For use of GEBCO’s grids in Esri ArcGIS Desktop packages, such as ArcMap, it is possible to import the data in a number of ways
- Esri ASCII raster data sets can be converted to Esri rasters using Esri ArcToolbox routine 'ASCII to Raster' from the 'Conversion' Toolbox. Alternatively, Esri ASCII raster files can be added directly into ArcMap.
- GeoTiff files can be added directly into ArcMap.
- For the 2D netCDF grids it is suggested that they are imported as a 'netCDF raster layer'. The 'make netCDF raster layer' routine can be found in the Multidimension toolbox in ArcToolbox. See Esri’s web site for further details.
- For the 1D netCDF grids you can use the GEBCO Grid Display software to export the data in Esri ASCII raster format. See the accompanying software documentation for further details. Data in this form can be converted to an Esri raster using the ArcToolbox routine ‘ASCII to Raster’ from the Conversion Tools toolbox.
Related BODC pages
|GEBCO Grid download||GEBCO Grid Display Software|
|GEBCO project at BODC|
Related external links
|GEBCO project web site||NetCDF Climate and Forecast Metadata Convention|
|netCDF||Esri ASCII raster format|