100% of the earth's ocean floor has been mapped to a maximum resolution of around 5 km.
The entire ocean floor has now been mapped to a maximum resolution of around 5 kilometers (3.1 miles), which means we can see most features larger than 5 kilometers (3.1 miles) across in those maps.
That's the resolution of a new global map of the seafloor published recently by David Sandwell of Scripps Institute of Oceanography in San Diego and colleagues, who used some nifty tricks with satellites to estimate the landscape of the seafloor and even reveal some features of Earth's crust lurking beneath sea-floor sediments.
Unlike mapping the land, we can't measure the landscape of the seafloor directly from satellites using radar, because seawater blocks those radio waves. But satellites can use radar to measure the height of the sea's surface very accurately.
And if there are enough measurements to subtract the effects of waves and tides, satellites can actually measure bumps and dips in the sea surface that result from the underlying landscape of the ocean floor.