Because each city or town is permitted to establish datums, the elevation point A) typically is an arbitrary number, such as "1 foot," because it is only a reference used for local elevations. B) is decided by the Army Corp of Engineers based on the average sea level of Galveston Bay. C) is decided by the U.S. Geological Survey and is the accurate local measurement of height above sea level in New. York Harbor. D) is only valid within a five-block radius of the benchmark, beyond which cities are obligated to reset their datum points back to zero (0).

The establishment of local datums has a rich history tied to the need for standardized measurements in various regions. Many cities initially used arbitrary reference points for construction and surveying, making the need for reliable benchmarks essential for infrastructure development. As urban areas grew, the demand for accurate elevation data also rose, leading to the establishment of more precise systems that help avoid confusion in construction and urban planning. In real-world applications, the use of local datums is crucial for civil engineering, architecture, and even environmental science. For instance, when building bridges or levees, precise knowledge of elevations ensures these structures can withstand flooding or other geological changes. Engineers and surveyors must be familiar with the specific datum used in their region to create safe and effective designs that account for local topography.