GEBCO global bathymetry grid

GEBCO (the General Bathymetric Chart of the Oceans) is a non-profit body working under the International Hydrographic Organization and UNESCO's Intergovernmental Oceanographic Commission.⁴ Its chart series began in 1903.⁴ It relies largely on volunteer geoscientists and hydrographers.⁴ Bathymetry is the measurement of the depth and shape of the seafloor.⁴ The Nippon Foundation of Japan proposed a partnership with GEBCO in 2016 to map the whole ocean floor by 2030, and the two now run it as the Seabed 2030 project.^2,4

The GEBCO Grid is a single terrain model of ocean and land, with heights and depths in metres on a 15 arc-second grid of 43,200 rows by 86,400 columns.^1,2 The current grid, GEBCO_2026, was published in April 2026.² It is built on the SRTM15+ dataset from Scripps Institution of Oceanography, which joins land heights with measured seafloor depths and depths predicted from satellite measurements of gravity.^2,3 Grids compiled from survey data, mostly multibeam sonar, by four Seabed 2030 regional centres are blended onto that base.^2,3 North of 60°N and south of 60°S the land and ice heights come from BedMachine models of Greenland and Antarctica and other polar sources.² One version gives the ice surface and a second gives the ground beneath the ice.^1,2

Alongside the depths comes a Type Identifier grid that says, cell by cell, what each value rests on: a direct measurement such as multibeam, singlebeam or lidar, an indirect one such as a gravity prediction or interpolation, or an unknown source.^2,3 GEBCO notes that the data are assumed to be relative to mean sea level, but some shallow-water sources use other vertical datums.^1,2

The grid is in the public domain and free, including for commercial use, and GEBCO asks that it be credited with a citation that carries its DOI.^1,2 It can be downloaded whole as netCDF or in eight tiles as GeoTIFF or Esri ASCII raster; the global netCDF file is 7 GB uncompressed.^1,2 A download app cuts out a chosen area, and the grids can also be read over OPeNDAP, a protocol for reading parts of remote files, through the UK's Centre for Environmental Data Analysis.¹ GEBCO takes contributions of singlebeam and multibeam survey data, individual soundings and existing grids to improve the grid.⁴

GEBCO lists what seafloor depth is used for: ocean circulation, tides, tsunami forecasting, fishing, sediment transport, geo-hazards, and routing cables and pipelines.⁴ For someone modelling a coast, a bay or a stretch of sea, it supplies the depths a tide, wave or circulation model needs as its floor.⁴ The Type Identifier grid shows where those depths were surveyed and where they were estimated.^2,3