Depth Contour

A line on a nautical chart joining points of equal charted depth relative to the chart’s vertical datum.

Also called an isobath, a depth contour helps depict the shape of the seabed and the boundary between depth bands. Closely spaced contours often indicate a steeper slope, but survey density, generalisation and chart scale limit how much detail the line represents.

The line does not show depth below the water surface at the time of use. Actual water depth requires the charted value to be combined with height of tide and other relevant allowances, and isolated dangers or soundings may be more restrictive than the surrounding contour.