Which system provides the geodetic datum for horizontal coordinates in this context?

• A. Continuously Operating Reference Stations (CORS) supported by NGS.
• B. Local bench marks only.
• C. Elevation data from local level networks.
• D. Global Positioning System satellites.

Answer: (A)

Understanding how horizontal coordinates get their precise reference requires a stable, nationwide reference frame. The Continuously Operating Reference Stations network, supported by the National Geodetic Survey, provides that frame. By collecting GNSS data from many fixed stations and adjusting them together, it defines a consistent horizontal coordinate system (such as NAD83) used across the country. This network ties field measurements to a common datum, enabling accurate, comparable positions over time and distance.

Local bench marks are individual physical markers and don’t establish a national datum. Elevation data relates to vertical control, not horizontal reference. GPS satellites provide observations, but the datum itself comes from the reference-station network and its network-wide adjustment, not the satellites alone.