What is the primary purpose of a theodolite?

The primary purpose of a theodolite is indeed to serve as a surveying instrument for measuring angles. This instrument is essential in various surveying tasks, specifically for determining horizontal and vertical angles. Theodolites are crucial for the establishment of control points, alignment tasks, and for various applications in construction and land surveying.

Their ability to measure angles accurately allows surveyors to create detailed and precise maps and plans. In many surveying projects, knowing the exact angles between different points is fundamental to establishing the geometry of the area under study, thus making the theodolite indispensable.

The other options relate to different surveying and measurement tools or techniques. For instance, measuring land area typically involves additional calculations or the use of specific software and is not the primary function of a theodolite. Aerial photography involves capturing images from the air, often using drones or aircraft, which is distinct from angle measurement. Lastly, calculating distances often uses methods like triangulation or electronic distance measuring tools, rather than being the direct function of a theodolite.