In 2011, the District of Columbia government commissioned a project to survey the Washington D.C. historic boundary stones set in 1791 and 1792 that define the Maryland and (then Virginia) border with the new Federal District. The majority of the stones were located using a field survey which employed a GPS-RTK. Surveyed accuracy is +/- 5cm horizontal and +/- 9cm vertical. The Washington D.C. Historic Boundary Stones were then connected to form the Washington D.C. Historic Boundary. However, this is not used for the planning, administration, or management of Washington D.C. The boundary stones do not form a perfect 10 mile by 10 mile square of DC, and are not perfectly aligned on each side. Given that they were placed over 200 years ago the survey is impressive, however they do not accurately reflect today's DC Administrative Boundary which was produced with more advanced methods and data.Excerpts from Boundarystone.org:The Residence Act of July 16, 1790, as amended March 3, 1791, authorized President George Washington to select a 100-square-mile site for the national capital on the Potomac River between Alexandria, Virginia, and Williamsport, Maryland. President Washington selected the southernmost location within these limits so that the capital would include all of present-day Old Town Alexandria, then one of the busiest ports in the country. Acting on instructions from Secretary of State Thomas Jefferson, Major Andrew Ellicott began his initial observations for a rough survey of the ten-mile square on Friday, February 11, 1791.Ellicott, a prominent professional surveyor, hired Benjamin Banneker, an astronomer and surveyor from Maryland, to make the astronomical observations and calculations necessary to establish the south corner of the square at Jones Point in Alexandria. According to legend, "Banneker fixed the position of the first stone by lying on his back to find the exact starting point for the survey ... and plotting six stars as they crossed his spot at a particular time of night." From there, Ellicott's team embarked on a forty-mile journey, surveying ten-mile lines first along the southwest line, then along The northwest line, next along the northeast line, and finally along the southeast line. The team completed this rough survey in April 1791.Ellicott's team then began the formal survey by clearing twenty feet of land on both sides of each boundary line and placing other stones, made of Aquia Creek sandstone, at one-mile intervals. The boundary stones are the oldest federal monuments. Although several stones have been moved or severely damaged, thirty-six stones from the 1790s are in or near their original locations, including all fourteen in the land that was returned to Virginia in the 1846-1847 retrocession. Three other locations have substitute stones (SW2, SE4, and SE8), and one location (NE1) is marked only by a plaque.Learn more at boundarystone.org.