Chart No. 1 · I 30
Depth contour
Depths & contours
A line joining points of equal depth, labeled with its depth; blue tints highlight the shallows.
What it means
Depth contours join soundings of equal depth (2, 5, 10, 20 m…), with the value set into a break in the line. The zero contour is the low-water line at chart datum.
Why it matters
Contours give the shape of the bottom at a glance. Many skippers pick a 'safety contour' (say 5 m) and treat everything inshore of it as out of bounds — a simple, powerful passage-planning habit.