CST Level 1 Land Surveyor Certification Practice

How many national datums are required to establish horizontal and vertical coordinates?

1. One national datum

2. Two national datums

3. Three national datums

4. Four national datums

The correct answer is: Two national datums

To establish horizontal and vertical coordinates accurately, it is necessary to use two national datums. The horizontal coordinate system is typically based on a geodetic datum, which provides a reference for measuring positions on the Earth's surface. In the United States, for example, the North American Datum (NAD83) serves this purpose for horizontal positioning. On the other hand, vertical coordinates require a different reference, commonly defined by a vertical datum, such as the North American Vertical Datum (NAVD88). This provides the necessary reference for measuring elevations or depths. Combining these two types of datums allows for a comprehensive system to define locations in three-dimensional space — one datum for positioning on the Earth's surface (horizontal) and another for elevation or depth (vertical). Thus, utilizing both a horizontal and a vertical datum is essential for ensuring accuracy and consistency in surveying and mapping practices.