Definition
Standard metric contours are drawn at 2, 5, 10, 20, 30, 50, 100 and 200 metres and beyond, with the shallower ones often given blue tint bands. Contours are interpolated from soundings and are therefore smoothed representations of the real seabed. In pilotage a chosen contour makes an excellent handrail, and a depth contour used as a limit not to be crossed is a clearing line that the echo sounder alone can monitor.
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