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 examples of 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 engineering, construction, and floodplain management. They help ensure that measurements are accurate and comparable across different regions, facilitating effective planning and decision-making in projects that involve land use and water management.