[gnarlysasquatch]

Aren’t there maps?

[brokenmachine]

Well, now the map of that area has one mountain on it.

[pugworthy]

Only where you go and record data to create said maps.

Sonar systems have not mapped the entire sea floor, and as others have pointed out, sonar is the main effective way to create such a map.

[alfalfasprout]

and running sonar in enemy waters is not exactly a good idea :)

[tbihl]

Charts. Yes, and arguably that's part of the problem. If everything is just 'charted', you lose sensitivity to the things that are old or low resolution because it's all on the same chart.