Sea depth — how this layer is made

What you are looking at

This map shows the depth of the sea floor everywhere in the world, coloured from the shallows to the deepest trenches. Land is left uncoloured, so whatever layer sits beneath shows through.

The scale is metres below sea level. The deepest colour is reserved for the trenches. Only a handful of places on earth go below 10,000 m, and the Challenger Deep in the Mariana Trench, at about 10,900 m, is the deepest of them.

Where the data comes from

The map is built from the GEBCO_2026 Grid, published in April 2026 by the General Bathymetric Chart of the Oceans under the Nippon Foundation–GEBCO Seabed 2030 project and archived by the British Oceanographic Data Centre. It is one continuous grid covering the whole world, with a cell about 463 m across at the equator and narrower towards the poles.

We build the tiles ourselves from that grid rather than pointing at somebody else's tile service, so the map does not depend on a third party staying online.

Most of the sea floor has never been measured

This is the most important thing on this page, and it is easy to miss when the map looks this complete.

As of April 2026, Seabed 2030 reports 28.7% of the ocean floor mapped to modern standards, roughly 104 million km². The rest is inferred from satellite altimetry. Rock pulls harder on the water above it than open water does, so the sea surface stands slightly higher over an underwater mountain and slightly lower over a trench. Satellites measure that shape, and the depth beneath is estimated from it.

So a single resolution figure for this map would be false. Over a surveyed continental shelf, 463 m is honest. Over deep ocean the underlying soundings may be tens of kilometres apart, and what you see between them is interpolation. The map does not distinguish the two, and it does not look any less confident where it is guessing.

Colour

There are three schemes, and all of them run from pale in the shallows to dark in the deeps. None is evenly spaced. Most of the ocean floor is abyssal plain between about 3,000 and 6,000 m, so an evenly spaced scale would render four fifths of the sea as one flat tone.

Each scheme spends its colour somewhere different, and the numbers in the key change with it. Ocean covers the full range. Shallow puts nine of its eleven steps in the top 200 m, where continental shelves, sandbanks and approaches to harbours are. Deep does the opposite and reserves almost everything for the abyssal plain and the trenches. Relief shading is drawn over all three, and it is what makes ridges and seamounts legible rather than smooth.

Where the sea meets the land

The coastline you see is the basemap's, drawn from a different source at a much finer resolution than 463 m. This layer traces it with a dark line, because shallow water and low-lying land can otherwise be almost the same colour. Around Hawaii, or the Wash, the shore is hard to find without it.

The two sources do not agree everywhere. At high zoom on a complicated coast, such as a Norwegian fjord or a river mouth, the colour may stop slightly before or after the drawn shore.

Land is set to exactly zero and left uncoloured. One consequence is visible and deliberate. Land that lies below sea level is painted as though it were sea. The Caspian Sea is the largest case, and it is arguably correct. The Dead Sea shore, the Qattara Depression in Egypt and Death Valley are smaller, and they are simply wrong. They are dry land shown in the colour of shallow water.

Which edition

GEBCO publishes annually, and each release moves depths as new surveys arrive. This map is built from the 2026 grid. It is not a time series. A new edition replaces this one rather than joining it, because the changes describe better knowledge rather than a changing sea floor.

Known weaknesses

Beyond the coverage problem above, depths are rounded to whole metres, which is far finer than the data warrants. Below-sea-level land is painted as sea. The finest zoom holds about 306 m per pixel, and zooming closer magnifies that rather than revealing anything more.

Source and licence

GEBCO Bathymetric Compilation Group 2026 (2026). The GEBCO_2026 Grid - a continuous terrain model for oceans and land at 15 arc-second intervals. NERC EDS British Oceanographic Data Centre NOC. doi:10.5285/4f68d5c7-45eb-f999-e063-7086abc036fa

GEBCO's grids are in the public domain and may be used freely. Not for navigation.