A vertical reference system is a method used to measure and define elevations or heights in relation to a specific baseline. This baseline is often referred to as a datum, which serves as a starting point for measuring vertical distances. Common examples of vertical reference systems include the North American Vertical Datum of 1988 (NAVD 88) and the International Great Lakes Datum (IGLD). These systems are essential in fields like geodesy, civil engineering, and construction, as they provide a consistent framework for determining how high or low a point is relative to sea level or other reference points. Accurate vertical measurements are crucial for designing structures, mapping terrain, and ensuring safety in various applications.