The datum is defined by the observed heights of mean sea level at the 26 tide gauges and by the set of elevations of all bench marks resulting from the adjustment. A total of 106,724 kilometers of leveling was involved, constituting 246 closed circuits and 25 circuits at sea level.
George Washingtonâs Mount Vernon is located roughly 15 miles south of Washington, D.C. and 8 miles south of Alexandria, Virginia on the banks of the Potomac River, at the southern end of the George Washington Memorial Parkway.
Philadelphia and New York both have had the luxury of being our capitol up to this point. Washington's home, Mount Vernon was located on the Potomac and there was a confluence of the Potomac and another river 10 or 15 miles upstream. This is the site Washington picked for the federal district as it was referred to.