A vertical datum is a reference point or surface used to measure elevations and depths on the Earth's surface. It provides a consistent framework for determining how high or low a location is relative to sea level or other reference points. Common vertical datums include the North American Vertical Datum of 1988 (NAVD 88) and the International Great Lakes Datum (IGLD). Vertical datums are essential for various applications, including mapping, construction, and floodplain management. They help ensure that measurements are accurate and comparable across different regions. Understanding vertical datums is crucial for engineers, surveyors, and environmental scientists.