What does it mean that only 5% of the ocean floor is “mapped” and why is that number so small?

Question

I often see this statistic referenced, but I don’t understand exactly what it means. And why only 5 percent? Is it because of the ocean’s unfathomably massive size? The cost of mapping? It’s not worth mapping? All of the above?

In: Earth Science

Answer 1

The entire ocean floor has been mapped. The 5% is how much has been mapped by modern sonar.

https://oceanexplorer.noaa.gov/world-oceans-day-2015/how-much-of-the-seafloor-is-left-to-explore.html

80% of the ocean is still unexplored.

https://oceanservice.noaa.gov/facts/exploration.html#:~:text=More%20than%20eighty%20percent%20of,the%20mysteries%20of%20the%20deep.