What is the purpose of a plumb line in surveying?

The purpose of a plumb line in surveying is to determine verticality. A plumb line consists of a weight (often a plumb bob) suspended from a string, which is used to establish a true vertical reference. When the weight is allowed to hang freely, it will settle in a straight line toward the center of the Earth due to gravity, indicating what is truly vertical.

This is crucial in surveying for ensuring that structures are built straight up and down, which is important for both aesthetic and structural integrity. When setting up equipment or checking the level of various surfaces, the plumb line serves as a reliable guide for confirming that they align correctly in the vertical direction.

Other options, while relevant to surveying, do not pertain to the specific function of a plumb line. Measuring horizontal angles involves tools like theodolites, identifying land boundaries may require legal definitions and delineation methods, and calculating distances typically utilizes chains, tapes, or electronic distance measuring devices. Each of these tasks plays a significant role in the surveying process, but they do not directly involve the function of determining verticality that a plumb line provides.