Explain “horizontal control” in geodetic surveying.

Horizontal control in geodetic surveying involves establishing a network of horizontal reference points that serve as a foundation for determining the positions of other points on the Earth's surface. This network is crucial because it provides a consistent and reliable framework for mapping, construction, and land surveying.

The primary purpose of horizontal control is to ensure accurate spatial positioning and alignment of various features on the Earth's surface. These reference points are typically established using precise measurements from GPS or traditional surveying methods, and they can be used to derive coordinates for additional points within the network, facilitating accurate mapping and geographical assessments.

In contrast, the other options do not accurately capture the essence of horizontal control. The measurement of vertical angles pertains to vertical control and elevation determinations, while vertical lines reference heights, which is distinct from horizontal measurements. Adjusting geodetic data is a separate aspect of maintaining accuracy in surveying but does not specifically define horizontal control. Therefore, the correct answer highlights the foundational role that a network of horizontal reference points plays in effective geodetic surveying practices.