The vertical datum used by surveyors across the country is mean sea level, obtained through a tide gauge. You start somewhere and you say, ‘I know this number.’ In the case of measuring your height, you’re calling the floor zero.” “If you didn’t know that you’re measuring from where their feet touch the floor, you don’t have a good reference. You determine this by measuring from a person’s feet to the top of his or her head - the reference surface is the floor. He uses the example of measuring someone’s height. Zilkoski, the former director of the National Geodetic Survey at the National Oceanic and Atmospheric Administration and the man who helped supervise the monumental 14-year NAVD 88 project. “A vertical datum is just a reference surface,” says David B. To appreciate the ways in which the vertical datum ties the country together, it is helpful to know what it is. Zilkoski, the former director of the National Geodetic Survey at the National Oceanic and Atmospheric Administration, helped supervise the monumental 14-year NAVD 88 project. Army Corps of Engineers - will be replaced by a new, satellite-based system.ĭavid B. In a few years the key datum of the last 30 years, the North American Vertical Datum of 1988 - the datum used by federal agencies such as the Federal Emergency Management Agency and the U.S. In the late 19th century and through the early decades of the 20th, multiple vertical datums - the standard for accurate measurement of elevation across large distances - existed across the country.īut over time these datums became consolidated. In 19th century America, the expansion of the railroad famously led to the creation of our modern time zones, imposing temporal order on a nation that to that point set time by dozens of local “high noons.” In bridging east and west and transforming America into a continental nation, the railroads also shaped the development of geodetic surveying. Surveyors use a Fischer level at Glen Canyon in 1921.
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