Which term is the reference level for depths and heights on a chart?

• A. Reference level for depths and heights
• B. Water depth in feet, fathoms, or meters
• C. Difference between true north and magnetic north
• D. Estimating position using course and speed

Answer: (A)

The reference level for depths and heights on a chart is the chart datum—the zero line used as the baseline from which all depths (soundings) and elevations are measured. This provides a consistent frame of reference across the chart so a depth shown is interpreted in relation to the same zero everywhere on the map. The term described by the option captures this idea: it’s about the baseline used to express depths and heights.

The other ideas point to different concepts: depths are shown in various units like feet, fathoms, or meters, which are about how the numbers are expressed rather than what they’re measured from; the difference between true north and magnetic north refers to magnetic variation; and estimating position using course and speed relates to dead reckoning. None of those describe the baseline zero for depths and heights.