Squares are calculated by the outer extents of the record or tax lots within a defined area (typically a city block). There are roughly 4896 active squares.
A Square is similar to a city block. Squares were numbered starting at 1 and are currently in the 6000 series. Not all squares are active. A common cause of squares becoming inactive has been through street closing and combining squares. When the squares are combined usually the lower square number is killed and the higher square number is used for the combined square.
For example if squares 1 and 2 are combined, square 1 is killed and the combination becomes square 2.
Spatial Location of Squares
- Each Square is an Island, alone unto itself. - There is not now, and has never been, any citywide Survey Coordinate System in D.C. - Most squares are unrelated to other Squares by “Measured.” They are related by Record. - Street width is approximate. You cannot rely on the published official street widths to set up property lines or determine right-of-way. There is digital scan information available from DDOT regarding Right-of-Way. - Some Squares are divided by streets. That is, the same Square continues on the other side of the street. - Since there is no citywide Survey Coordinate System, squares were placed in their approximate location. This process is known as “best fit”.
Once a square was COGO’ed/created it became a “floating island(s)” without geographic positioning. Because of this, captured VP data had to be positioned relative to other geospatial files that themselves are geo- referenced. The obvious choice was fitting them to the digital ortho’s and planimetrics compiled at a scale of 1:100 or 1inch = 83.3feet
- Squares were visually positioned over the appropriate area in of the orthophoto and planimetrics (ground level feature were primary source)**Note, row house firewalls are more accurate than building footprints because rooflines often hang into public space, this was determined during the VP pilot. Firewalls are corrected photogrammetrically, while the digital orthophotos could include additional uncorrected displacement up to several feet (elevated features, e.g rooftops are displaced outward from the center of digital orthophotos which are correct only for features at ground level).
Spatial accuracy: Squares should always be within 1.5 meters of the apparent position on the orthos.
Squares layers in VPM are (point, line, poly) - SquaresPT, SquaresLN, SquaresPLY, Squares_History_LN, Squares_History_PLY