Name common geodetic datums used in the United States for mapping and positioning.

• A. WGS84 for GNSS; state plane systems often use NAD83.
• B. NAD27 (historically) and NAD83 for mapping; WGS84 widely used for GNSS.
• C. ITRF and ETRS89.
• D. NAD83 (and NAD27 historically), and WGS84 for GNSS; state plane systems often use NAD83.

Answer: (D)

In the United States, mapping and positioning rely on two related but distinct threads of datums. NAD83 is the current standard for most mapping work and is the basis for the State Plane Coordinate System in many states. NAD27 is still encountered in older datasets and maps. For positioning with GNSS, the reference frame is WGS84, which is the framework used by GPS. These datums are not identical, so converting coordinates between them requires a datum shift. This combination—NAD83 (and NAD27 historically) for mapping and State Plane, and WGS84 for GNSS—reflects common practice in the U.S.