CST Level 1 Land Surveyor Certification Practice

Which system governs vertical coordinates and was updated from NGVD 29?

1. NAD 27

2. NAVD 88

3. NAD 83

4. EGM 96

The correct answer is: NAVD 88

The system that governs vertical coordinates and was updated from NGVD 29 is NAVD 88. NAVD 88, or the North American Vertical Datum of 1988, provides a more accurate and consistent reference for vertical measurements across North America compared to its predecessor, NGVD 29, which had limitations due to the technology and methods available at the time of its establishment. NAVD 88 utilizes a network of precise leveling data and adopts a geoid model that accounts for variations in the Earth's gravitational field, allowing for improved accuracy in the determination of elevations. This makes it the standard for vertical datums in surveying, ensuring that elevations measured under this system can be confidently compared across different locations and over time, thus facilitating various applications in engineering, construction, and geographical analysis. In contrast, the other options—NAD 27 and NAD 83—are horizontal reference systems, with NAD 27 being an earlier horizontal datum and NAD 83 representing an update to better reflect the Earth's size and shape. EGM 96 refers to a model of the Earth's gravity field, which helps in geoid determination, but it is not a vertical datum in itself. Thus, NAVD 88 is essential for accurate vertical measurements in land surveying contexts