To revive a long-dead thread with a bit of news, there is a project to map the ocean floors, and I mention this here mainly because it offers a case for comparison with the mapping of other bodies.
https://seabed2030.org/faqThe goals are, in comparison with our maps of other worlds, shockingly modest – to map the depth of most of the ocean floors at a resolution of only 400 meters per element. Thus far, the project is about 21% complete, but the organizers express hope that it will nonetheless be complete by 2030 (hence the name).
This may be interesting to compare with the mapping of, say, Venus by Magellan.
Of course, unlike the surfaces of other worlds, we have the opportunity to perform in situ exploration of the oceans at specific points on an extremely widespread basis.