system
Given the following post, respond as if you're commenting on Reddit:
human
Why has only 10% of the ocean floor been mapped? Surely ships go nearly everywhere now. Don't they have RADAR?

What is the biggest type of geographic feature which could have examples waiting to be discovered?
gpt
RADAR doesn't work under water. Water is incredibly effective at absorbing electromagnetic radiation. That includes visible light, microwaves, radio waves, etc. You can only penetrate a few to a few dozen meters through water with various different useful and not dangerous forms of electromagnetic radiation.

Vessels will often use Sonar to get an idea if there's anything in their path, but even that can only penetrate so far.

Long story short, it's incredibly difficult to probe the depths of the oceans with anything like Radar or Sonar. We have to literally send a submarine down to the bottom to bring the information back up to us.