Which method is commonly used for measuring long distances in surveying?

The electronic distance measurement (EDM) method is commonly used for measuring long distances in surveying due to its precision and efficiency. EDM devices calculate distances by using the time it takes for a signal, typically a laser or radio wave, to travel to a target and back to the instrument. This method allows for rapid measurements over great distances, which is essential for modern surveying practices that require accuracy and the ability to cover extensive areas in a short amount of time.

Compared to other methods, EDM is highly accurate and can be used in various conditions, including less-than-ideal weather, making it a preferred choice in many surveying applications. The technology behind EDM has improved significantly and is associated with automated data collection, which reduces human error and increases reliability.

Other methods, such as optical rangefinders, while useful for shorter distances or specific applications, may not provide the same level of precision or efficiency over long distances. Triangulation is a fundamental concept in surveying but requires multiple measurements and can be less effective in areas where clear lines of sight are not available. The string line method is limited to smaller measurements and is more applicable in construction or layout tasks rather than surveying long distances.