A small number printed on a chart, giving the depth of water at that point.
Also known as: Numbers on a sea chart
The numbers scattered across a chart are depths, measured from a datum low enough that the real depth is almost always greater. That conservative choice is deliberate: a chart that erred the other way would run vessels aground.
States the depth of water at that point, measured below the chart datum rather than below the surface at any given moment.
Contexts: Navigation
Is referenced to a datum set near the lowest tide that occurs, so the actual depth is almost always greater than printed — an error deliberately made in the safe direction.
Contexts: Navigation
Is printed in metres on modern charts and in fathoms on older ones, which is why the units are always stated in the chart's title block.
Contexts: Navigation
A small numeral, sometimes with a subscript digit for the decimal, printed directly on the charted water area without any enclosing shape.
Depth contours join soundings of equal value, as land contours join heights.