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The Boundary Markers of the Original District of Columbia are the 40 milestones that mark the four lines forming the boundaries between the states of Maryland and Virginia and the square of 100 square miles (259 km²) of federal territory that became the District of Columbia in 1801. A survey team led by Major Andrew Ellicott placed these markers in 1791 and 1792; among Ellicott's assistants were his brothers Joseph and Benjamin Ellicott , Isaac Roberdeau, George Fenwick, Isaac Briggs and astronomer Benjamin Banneker.〔 ''at'' (boundarystones.org )〕〔(1) (2) At Google Books.〕 Today, 36 of the original marker stones survive as the oldest federally placed monuments in the United States. Due to the return of the portion of the District south and west of the Potomac River to Virginia in 1846, some of these markers are now within Virginia. ==Geography== The District of Columbia was originally specified to be a square in area, with the axes between the corners of the square running north-south and east-west, and having its southern corner at the southern tip of Jones Point in Alexandria, Virginia, at the confluence of the Potomac River and Hunting Creek (later the site of the Jones Point Lighthouse).〔 At Google Books.〕 The sides of the square are each long. The specified orientation results in a diamond shape for the District's original boundaries on most maps. The north-south axis of the District's current boundaries extends between present 17th and 18th Streets, N.W., continuing south across the National Mall to the far shore of the Potomac River; the east-west axis is between present Constitution Avenue and C Street, N.E. and N.W.〔The north-south axis is a straight line connecting the north and south cornerstones of the original District of Columbia. The east-west axis is a straight line connecting the east and west cornerstones of the original District of Columbia.〕 Note that these axes are not the lines used to define the four geographical quadrants of the District (N.E., N.W., S.E., and S.W.), commonly appended to Washington street addresses, which are delimited generally by North Capitol Street, East Capitol Street, South Capitol Street, and the National Mall. The center of the square is west of the Ellipse and north of the Mall, within the grounds of the headquarters of the Organization of American States.〔Coordinates of the center of the square of the original District of Columbia: . The center of the square of the original District of Columbia is the crossing of the north-south axis line and the east-west axis line.〕 In 2011, the District of Columbia geographic information system (GIS) program completed a project to map the District’s boundary using Global Positioning System (GPS) and contemporary survey technology at an accuracy of +/- horizontally and +/- vertically. The GIS program's survey found that (listed in the order in which Andrew Ellicott's team performed the initial boundary survey): * Along the northwest boundary, the stones are outside the existing boundary ranging from to * Along the northeast boundary, the stones are inside the existing boundary ranging from to * Along the southeast boundary, the stones are outside the existing boundary ranging from to The overall accuracy of the historic survey and the survey using 2011 technology produced remarkably similar results. For example, the distance between Southeast stones numbers 6 and 7 is , almost exactly one mile (). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Boundary Markers of the Original District of Columbia」の詳細全文を読む スポンサード リンク
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