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.
A modern reconstruction of Washington's wharf is located adjacent to the Pioneer Farm. Visitors can travel to Mount Vernon via boats departing from Washington, D.C., Alexandria, Va., and National Harbor, Md., or enjoy a 45-minute sightseeing cruise. Cruises are offered April to October (tickets available online, at the Orientation Center and aboard the boat).