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. 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. 

But over time these datums became consolidated. In a

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