Daily Dose · Maps / Oct 5, 2026 / Seafloor Mapping
The Floor We Haven't Seen
Ships have swept sonar across only 28.7% of the ocean floor. The rest of Earth's largest landscape is known only as a blur inferred from space.
71.3%
of Earth's seafloor has never been measured directly to modern standards — roughly 258 million km² (derived), more than all the continents combined.
SEABED 2030 / GEBCO · APR 2026 · 100 − 28.7
SEABED 2030 / GEBCO · APR 2026 · 100 − 28.7
01 · Progress
From 6% to 28.7% in nine years
The global effort has nearly quintupled the mapped share since 2017. But the 2030 deadline is four years away.
Last year added ~5 million km², a record, and lifted coverage by 1.4 points. To finish by 2030, the world would need roughly 18 points a year, about 13 times faster. At the 2025–26 pace, the job takes another ~51 years. (Projections are simple arithmetic.)
02 · What “mapped” means
The deeper the water, the coarser the target
Sonar footprints widen with depth, so Seabed 2030 sets a sliding standard: one depth value per 100 m grid cell near shore, per 800 m in the trenches.
Most of the ocean sits in the 3,000–5,750 m band, where a cell is 400 m across. The average depth is 3,682 m. The deepest known point, Challenger Deep, is about 10,935 m down.
03 · Sharper elsewhere
We have crisper global maps of Mars
Where no ship has passed, our best picture of the seafloor comes from the ocean's surface bulging over mountains, which satellites can measure only at kilometre scale.
Grid spacing is plotted on a log scale, so shorter bars mean sharper maps. Mars has a complete laser-altimeter grid at ~463 m. The unsurveyed seafloor is known at about 8 km, from the SWOT satellite (2024), which is still twice as sharp as the 30-year satellite record it replaced. A seamount smaller than a few kilometres can stay invisible.
04 · The bill
Two hundred ship-years
The numbers that set the scale of finishing the map.
~200
ship-years of multibeam surveying to map the remaining seafloor
Mayer · ASA 2020
$3–5 bn
estimated total cost of finishing with today's sonar technology
Mayer · ASA 2020
220
organisations now contribute data to Seabed 2030, 15 of them new in the past year
Seabed 2030 · 2026
05 · Stakes
Blank charts have consequences
Bathymetry drives tsunami models, cable routes, fisheries, ocean-mixing physics and safe navigation.
2005
USS San Francisco ran into a seamount missing from its chart, ~350 nmi south of Guam. One sailor died.
US Navy
6.4→20.5%
coverage jump in the ROPME Sea Area (Gulf region) in a single year of new contributions
Seabed 2030 · 2026
104M km²
now mapped to modern standards, roughly 7 times the area of Antarctica
Seabed 2030 · 2026
What to notice on the map
Follow the bright lines
- Coasts glow, centres go dark. Shelves near wealthy ports are surveyed again and again. Open-ocean coverage is mostly single transit lines.
- The north is brighter than the south. The South Pacific and Southern Ocean are the planet's largest blanks.
- Regions can leap. The ROPME Sea Area tripled its coverage, from 6.4% to 20.5%, in a single year of new contributions.
- Look for the amber. The Mid-Atlantic Ridge, Challenger Deep and the San Francisco seamount all sit in water where good charts matter.
Sources & notes
- Seabed 2030 / GEBCO (IHO & IOC-UNESCO) progress update, 28 Apr 2026: 28.7% of the seafloor mapped to modern standards; ~104 million km²; ~5 million km² added in a year; 220 contributing organisations; ROPME Sea Area 6.4% → 20.5%.
- Seabed 2030 annual announcements: 6% (2017 launch), 15% (2019), 20.6% (2021), 23.4% (2022), 24.9% (2023), 26.1% (2024), 27.3% (Jun 2025).
- Mayer et al. (2018), “The Nippon Foundation–GEBCO Seabed 2030 Project,” Geosciences 8(2):63 — target grid resolution by depth (100 / 200 / 400 / 800 m).
- L. Mayer, Acoustical Society of America (2020), “Can we map the entire global ocean seafloor by 2030?” — ~200 ship-years and US$3–5 billion to finish with multibeam sonar.
- Yu, Sandwell et al. (2024), Science — SWOT satellite seafloor gravity map at ~8 km resolution. Smith & Sandwell (1997), Science — earlier altimetry bathymetry at ~12.5 km grid spacing (W.H.F. Smith & Sandwell, Oceanography 2004).
- NASA PDS: MOLA Mars global grid 128 px/deg (~463 m); LOLA lunar global grid 256 px/deg (~118 m).
- Stewart & Jamieson (2019), Earth-Science Reviews — Challenger Deep ~10,925–10,935 m (deepest measured). Charette & Smith (2010), Oceanography — mean ocean depth 3,682 m.
- US Navy / NTSB accounts of USS San Francisco (SSN-711), 8 Jan 2005: struck an uncharted seamount ~350 nmi south of Guam; one sailor killed.
- NOTES: The map is schematic and hand-drawn; swath patterns are illustrative of the known coverage pattern, not plotted from GEBCO source data. “71.3% unmapped” = 100 − 28.7. The 2030 dashed lines (≈18 pts/yr needed; ≈34% at the 2025–26 pace of 1.4 pts/yr; ≈51 years to finish at that pace) are simple arithmetic projections, not forecasts.