General Bathymetric Chart of the Oceans (GEBCO)

Data export formats

GEBCO Digital Atlas

The vector and gridded data sets can be exported through the GEBCO Digital Atlas (GDA) Software Interface. Formats are included that are compatible with the Generic Mapping Tools (GMT) system, Environment Systems Research Institute (ESRI) and AutoCAD software packages. The following relates to export from the GDA using version 2.12 of the GDA Software Interface.

  1. Exporting GEBCO's gridded bathymetric data sets
    1. ASCII format
    2. NetCDF format
  2. Exporting the vector data sets
    1. ASCII format
    2. DXF format
    3. Shapefile format
    4. Ordering the vectors
    5. Contiguity of vectors

For users not able to make use of the GDA Software Interface, the Centenary Edition of the GDA disc set includes a CDROM which contains a directly accessible set of files.

1. Exporting GEBCO's gridded bathymetric data sets

The complete GEBCO_2014 Grid, GEBCO_2014 Source Identifier (SID) Grid and GEBCO One Minute Grid files (or any subsets) may be exported in a simple ASCII format or as a netCDF file. Data exported in netCDF are suitable for use with the Generic Mapping Tools (GMT) system.

The elevation values are stored as signed 2-byte integers with the convention that bathymetric depths have negative values and topographic heights have positive values.

1.1 ASCII format

The following options are available.

Export the data in the format: longitude, latitude and elevation. Longitude and latitude formats may be selected from the following options

Export the elevation data only, as either one data point per line or one row of data per line. In the latter case, the data values may be separated by commas, spaces or output in a fixed-width format.

An additional option is available to export the data in an ASCII form that can be converted to an ESRI raster file using ESRI data conversion software. The data are exported in the form of rows with one row of data per line. The file includes header information in the required format for the conversion of the data file to an ESRI raster. The grid points are read eastwards from the Northwest corner of the selected data area.

1.2 NetCDF format

The GEBCO gridded data sets are stored in netCDF as a one dimensional array of 2-byte signed integers that represent integer elevations in metres. The data start at position 90°N 180°W and increase eastward.


2. Exporting the vector data sets

The vector data sets include bathymetric contour, coastline and trackline control data. The vectors may be exported in the following formats

In the data files, latitude is stored in the range -90° to +90° with north positive and south negative. Longitude is stored in the range -180° to +180° with east positive and west negative. However, the user can specify that the longitude data are stored in the range 0° to 360°.

2.1 ASCII format

ASCII files are built up as a series of labelled vector streams relating to bathymetric contours, coastlines, tracklines, survey box outlines or sounding points. A new vector stream is started for each contour segment, coastline segment, trackline, survey box outline or isolated sounding point.

Each vector stream consists of coordinate pair records preceded by a header record containing

Note that the '>' character was not included in previous versions of the GDA ASCII export format. Each coordinate pair is stored in a record with a geographic latitude 'ALAT' and longitude 'ALONG', expressed in decimal degrees.

Each 20-byte record is made up of a

Header record — IFLAG, ICODE, ICOUNT in format (A1,2I6,5X),CR,LF
Coordinate pair record — ALAT, ALONG in format (F8.4,F10.4),CR,LF

The feature code definitions are

Codes '1', '2', and '22010' to '22100' correspond to Antarctic related coastlines. Codes '1' and '2' are only present when the user has requested that feature codes '22010' to '22023' and '22090' and '22100' should be combined into code '1' and feature codes '22030' to '22050' into code '2'.

2.2 DXF format

DXF originated as a proprietary format in the commercially available 'AutoCAD' package, but is now a standard input format for many other commercially available software packages.

In DXF, the vector streams are expressed as polylines in geographic coordinates with each contour depth and coastline feature type assigned to a separate layer and a separate logical colour. Likewise, separate layers and logical colours are also assigned for tracklines, survey boxes and the position of isolated sounding points. The latter are expressed as type point rather than polylines. Each of the layers is labelled using the feature code definitions listed in the ASCII format definition above.

2.3 Shapefile format

This format is used by ESRI products such as ArcInfo.

Line and point feature types may be exported in ESRI Shapefile format. Bathymetric contour, coastline and trackline data are exported as line feature types and the position of isolated soundings as point feature types. Line and point feature types are exported to separate files.

2.4 Ordering of vectors

Vector data may be exported in ordered form. Ordering is by feature code. Thus any '0', '1' or '2' coastline vectors will appear before the bathymetric contour vectors which, in turn, will be arranged in ascending order of their depths. If present, the detailed Antarctic coastlines will follow the bathymetric contours and then be followed by tracklines, survey box outlines and isolated sounding points.

2.5 Contiguity of vectors

Within the GDA system the vector data sets are split into ten degree squares. The user can select to join up the vector segments on export. This option is only available if the user has selected to save the data in ordered format as described above.


Related GEBCO Digital Atlas pages at BODC

GEBCO Digital Atlas (GDA) introduction      Copyright and attribution
Contents      Order the GEBCO Digital Atlas
Software interface      Data set errata
Sample images Software Interface updates
GDA development  

Related GEBCO project pages at BODC

GEBCO at BODC      GEBCO Web Map Service (WMS)
Project overview GEBCO Grid display software
GEBCO world map IHO-IOC GEBCO Cook Book
Download data — GEBCO's gridded bathymetric data sets  

Related external links

Official GEBCO web site      Network Common Data Form (netCDF)
International Hydrographic Organization (IHO)      Environmental Systems Research Institute (ESRI)
Intergovernmental Oceanographic Commission (IOC)      AutoCAD
Coastline for Antarctica — Antarctic Digital Database (ADD)      Generic Mapping Tools (GMT)