Which geographic or mapping term best matches the description: a plane to which depth measurements are referred; used in depth curves?

Which geographic or mapping term best matches the description: a plane to which depth measurements are referred; used in depth curves?

• A. Sounding datum
• B. Mean sea level
• C. Tide datum
• D. Cartographic datum

Answer: (A)

Depth curves are based on depths measured against a fixed reference surface. That fixed plane is the sounding datum, a vertical reference used in hydrography so depths have a consistent meaning even as tides rise and fall. Mean sea level, while used as a reference for elevations on land, isn’t the standard reference for depths in charts. Tide datum refers to specific water levels (like mean high or mean low water) and isn’t the general reference plane for all depth measurements. Cartographic datum covers map position and sometimes vertical reference, but the term that best matches the description of a plane to which depths are referred for depth curves is sounding datum.

Depth curves are based on depths measured against a fixed reference surface. That fixed plane is the sounding datum, a vertical reference used in hydrography so depths have a consistent meaning even as tides rise and fall. Mean sea level, while used as a reference for elevations on land, isn’t the standard reference for depths in charts. Tide datum refers to specific water levels (like mean high or mean low water) and isn’t the general reference plane for all depth measurements. Cartographic datum covers map position and sometimes vertical reference, but the term that best matches the description of a plane to which depths are referred for depth curves is sounding datum.