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> I'm also surprised there's no contour lines between the depths (although perhaps this is done to not infer a knowledge of depths in the intermediate points wh
by chiph 5y ago
> I'm also surprised there's no contour lines between the depths (although perhaps this is done to not infer a knowledge of depths in the intermediate points where perhaps there is no such knowledge).
Yes, contour lines would imply accuracy that isn't there. The depth numbers indicate positions where the depth was actually measured. Any other location that doesn't have a number was not measured. Bear in mind that even if you have a depth number on your chart, it might be old and out of date. Safe navigation is never guaranteed. And subs never run depth-finder sonar when on patrol.
- AnimalMuppet 5y agoHow do depth numbers get out of date? Sedimentation? Underwater volcano eruption? Continental drift?
- zentiggr 5y agoThe broken assumption thee is that the ocean floor doesn't change. Things are changing all the time. Faster and faster as you get shallower and shallower. Shipping channels and shallows need to be resurveyed constantly or you have no idea what you might encounter.
- hugh-avherald 5y agoIt's also worth noting that the waters where depth accuracy is most important to a submarine are also the places where the depth is more likely to change (estuaries, ports, especially new/expanding/busy ports).
- chiph 5y agoTides & currents moving the bottom (sand, etc.) around, mostly. But it's also possible for a coral reef to have grown taller. Or a volcano, I suppose. :) NOAA's Chart No. 1 explains the symbols used on charts. https://www.nauticalcharts.noaa.gov/publications/docs/us-chart-1/ChartNo1.pdf https://www.nauticalcharts.noaa.gov/publications/docs/us-cha...