Which line would you consult to identify lines of equal water depth on a map?

• A. Depth curve.
• B. Underwater contour.
• C. Isobar.
• D. Tide line.

Answer: (A)

Lines that connect points of equal water depth on a map are depth contours, also called bathymetric contours. They show how deep the water is at each line, and the spacing between them indicates how steep the seafloor slopes—the closer the lines, the steeper the slope. This is what you’d consult to identify areas of equal depth and to gauge depth variation across a region, which is essential for navigation and planning. A line called an isobar marks equal atmospheric pressure, not depth, so it’s not about how deep the water is. A tide line denotes a water level at a particular tidal state, not the seafloor depth. And while some maps might use a descriptive phrase like underwater contour, the standard term used for lines of equal depth is depth contour.