Horizontal control surveys, whenever feasible, are based on which type of observations?

• A. Drone photogrammetry only
• B. Parcel boundary measurement by tape
• C. High-precision static GPS observations
• D. Quick single-precision leveling

Answer: (C)

Horizontal control surveys rely on measurements that establish precise, stable x,y coordinates tied to a geodetic reference. High-precision static GPS observations provide centimeter-level accuracy by observing satellites over extended periods, which allows accurate determination of baseline vectors between known points and creates a durable, globally referenced control network. This makes it the best choice when feasible for building a reliable horizontal framework.

Drone photogrammetry can map and extract features but isn’t typically the primary source of geodetically tied horizontal control, since its results depend on a checked network and aren’t inherently as stable as long-duration GPS in establishing a control framework. Parcel boundary measurement by tape is a local method prone to human error and environmental factors; it lacks the wide-area precision and consistency needed for a control network. Quick single-precision leveling concerns vertical differences and does not establish horizontal positions.

So, the preferred method is high-precision static GPS observations because they deliver the most accurate, reference-ready horizontal coordinates for a survey control network.