On a nautical chart, not all of the sea is known equally well. Some of it was surveyed last year by multibeam sonar; some was last sounded by a weighted line over the side of a boat in 1880. So charts carry a Zone of Confidence, a ladder of stars on each patch of water, six for "fully surveyed, trust it" down to a bare U for "nobody has checked."
The confidence is drawn straight onto the data. No methodology section, no footnote about survey vintage. You glance and you can see which parts to trust, compressed into an icon a tired navigator can read at three in the morning.