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Historic Review of the District’s Boundary Stones Using GPS and Modern Survey Technology

Tuesday, November 1, 2011
Accurately mapping the District of Columbia boundary for the DC GIS

The borders of Washington, DC were originally surveyed and marked with 40 stones by Andrew Ellicott in 1791 and 1792.  The first stone was placed at Jones Point in Alexandria by Benjamin Banneker, who calculated the southern corner of what would be the Washington, DC “square.”  From here Andrew Ellicott and his team surveyed one-mile increments along a line to the northwest, then the northeast, next southeast and finally back southwest to the starting point.  Currently, 38 of these boundary stones are in place, while the 39th is in storage and the 40th is marked by a plaque.

The District of Columbia GIS program recently completed a project to accurately map the District’s boundary using GPS and modern survey technology at an accuracy of +/- 5cm horizontally and +/- 9cm vertically.  Although the project’s intention was not to re-establish the District’s official boundary line, the results have produced valuable collaboration amongst District agencies, and also neighboring jurisdictions who are using the data to re-evaluate their own.  So how well do the stone locations align with the current DC Geographic Information System (GIS) boundary line?  Well, if you just “connect the dots/stones” you would find that:

• Along NE, the stones are inside the existing boundary ranging from 6.6’ to 18.4’
• Along SE, the stones are outside the existing boundary ranging from 12.75’ to 18.48’
• Along NW, the stones are outside the existing boundary ranging from 4.43’ to 9.6’

In other words, the overall accuracy of the historic survey and the recent survey using modern day technology produced remarkably similar results.  For example, the distance between Southeast stones numbers 6 and 7 is 5,280.824 feet; almost exactly one mile.

The results of the survey were used by the DC Surveyor’s Office to perform a comparison analysis against the current “GIS boundary” dataset used throughout the District government; and subsequently identify whether a new GIS boundary line is warranted.  The newly surveyed dataset is now a part of the District’s GIS database available for public and agency consumption.  Analysis results of the two boundaries show the data lines up very well with DDOT’s Right of Way polygon dataset (Eastern/Southern/Western Avenue etc).  Moving forward, DC data will be nested to the newly surveyed DC boundary.