What are the primary components of a sounding line?

A sounding line is traditionally used in nautical contexts to measure the depth of water, and its primary component consists of a line or rope attached to a weight at the bottom. The weight sinks to the seabed, allowing sailors to determine the water depth by pulling the line up and measuring its length. Using a sounding line is a fundamental practice in navigation, especially before the advent of modern electronic depth measurement tools. This method provides an accurate, direct measurement of the depth beneath a vessel, which is crucial for safe navigation in shallow waters.

The other options do not describe the essence of what a sounding line is. The mention of a map pertains to charting depth changes rather than measuring them directly. An electronic device for underwater imaging refers to modern technology that serves a different function than a traditional sounding line. Lastly, while a rope used for anchoring is important for securing a vessel, it does not pertain to measuring water depth. Thus, the understanding and function of a sounding line are accurately captured by the option that describes its physical properties and intended use.