The whole seafloor has a satellite-based map, but only a minority has been surveyed in high resolution. NOAA reports that 28.7% of the global seafloor had been mapped with modern multibeam sonar as of April 2026 [1].
Key takeaways
- Satellites cover the whole seafloor, but give only a general picture with limited detail.
- As of April 2026, 28.7% of the global seafloor had been mapped with modern high-resolution multibeam sonar.
- This map uses the GEBCO_2026 grid, which blends ship surveys with satellite estimates at 15 arc-seconds.
- Mapped is not the same as explored: people have seen far less of the deep seafloor than has been mapped.
How the seafloor gets mapped, and what "mapped" means
There are two answers to this question, and the gap between them is the whole story. Satellites have given us a map of the entire seafloor, but one with limited detail [1]. Ships fitted with modern multibeam sonar give a much sharper picture, but they can only survey the patch of water under and beside them. As of April 2026, 28.7% of the global seafloor had been mapped to that high standard [1].
That is a snapshot. The figure rises as surveys are finished and shared, so any number should be quoted with its date. Within it there is a big spread. Coasts, ports and shipping lanes are far better mapped than remote mid-ocean areas, because someone had a reason to look.
The Nippon Foundation-GEBCO Seabed 2030 Project exists to close the gap. It was formed by the Nippon Foundation and GEBCO as a call to produce a definitive map of the ocean by 2030 and make it available to all [2]. Its regional centres collect gridded depth data, and its global centre, in Liverpool, passes them to the GEBCO ocean map [2].
The homepage explains the methods in a few paragraphs. This page is about the size of the gap, and what it means for the picture you see on screen.
An example from our data
The grid behind this map is the GEBCO_2026 release. It holds a depth or height every 15 arc-seconds, and it uses a satellite-based dataset as its base, with the regional grids of Seabed 2030, largely based on multibeam data, added on top [3]. So some cells come from ship surveys and some are satellite estimates.
You can see the effect on the map. In places that have been surveyed, such as a coastal shelf, narrow canyons and ridges look sharp. Look at the open Pacific Ocean, where the mean depth is 4,315 m, and the seabed looks smoother, because large parts of it rest on estimates. The Mariana Trench is a good place to remember that even its deepest cell, 10,931 m, is a grid value, and published figures differ by tens or hundreds of metres.
That is also why we do not claim the map is a survey. It is a compilation, and the accuracy section of the homepage says so.
The thing people get wrong
The most common mistake is to read "mapped" as "explored". A map tells you the shape of the bottom. It does not tell you what is living there. NOAA says explorers have directly seen less than 0.001% of the deep ocean seafloor, and that more than 90% of the ocean is deep ocean, deeper than 200 metres [1].
A second mistake is to think a bigger percentage means a finished job. High-resolution coverage of 28.7% leaves most of the seabed without it, and even satellite coverage hides features such as seamounts and shipwrecks [1].
Mapped vs explored
| Mapped | Explored | |
|---|---|---|
| What it means | The shape and depth of the seabed has been measured | People or robots have seen the place and its life |
| How | Sonar from ships, satellite estimates | Dives, submersibles, remotely operated vehicles |
| Tells you | Where the ridges, trenches and plains are | What is living there and how it behaves |
Frequently asked questions
Is the whole ocean floor mapped?
Every part of it has a coarse satellite-based map, but only a minority has been mapped in high resolution by ships. The rest is estimated.
Why does the percentage keep changing?
Because ships keep surveying and handing in data. Any figure is a snapshot with a date, so check the date before you quote it.
Can I trust the detail on this map in remote areas?
Trust the big shapes. Where the grid rests on satellite estimates, it cannot show anything much smaller than a few kilometres across.
Sources
- How much of the ocean has been explored?, NOAA Ocean Service.
- Seabed 2030, The Nippon Foundation-GEBCO Seabed 2030 Project.
- GEBCO_2026 Grid, GEBCO.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against GEBCO_2026 grid).