Which instrument is commonly used for measuring horizontal angles in surveying?

The theodolite is the instrument commonly used for measuring horizontal angles in surveying due to its precision and design. It consists of a movable telescope mounted on a base that can be rotated both horizontally and vertically. This allows surveyors to accurately measure angles between reference points and establish control points in the field. The theodolite can measure both horizontal and vertical angles, making it a versatile tool for various surveying tasks.

In contrast, measuring tapes are primarily used for linear distance measurements and are not suited for angle measurement. Levels are designed to establish a horizontal plane and measure vertical angles, but they do not provide the capability to measure horizontal angles accurately. GPS receivers are primarily used for positioning and obtaining coordinates and do not measure angles in the way that a theodolite does. Thus, the theodolite's unique functionality makes it the appropriate choice for measuring horizontal angles in surveying.