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Delaware State and County Boundaries

Delaware State and County Boundaries
Primary Data Category:
Reference Basemap
Publication Date:
Jan 2004
Update Status:
Completed
Summary:

Three datasets are included: the official state boundary line, the county boundary lines, and the land/shore outline. These geospatial data files comprise the bounding lines relating to the political boundary delineation for the State of Delaware as well as the shoreline taken from the 2002 orthophotos of Delaware.

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Geography
Accuracy Information

No formal horizontal positional accuracy testing has been performed to qualify or validate these data. The horizontal positional accuracy of the source data used to generate this boundary varies greatly. Accordingly, the placement of boundary lines on land are generally more horizontally accurate and reliable than the position of boundary lines as they exists on large water bodies such as the Delaware Bay and the Atlantic Ocean. These boundary lines are positoned so they are coincident with known boundary monuments and boundary points. Boundary monument positions were based upon NGS coordinates as documented in several joint agreements between the States of Delaware, New Jersey, Maryland and Pennsylvania. These monument positions were stated to be within first and second order horizontal network accuracy. Not used were the computed boundary points and boundary reference monument positions from "Exhibit C" of the Joint Agreement between Delaware and New Jersey along the 1934 mean low water line (20010829). Boundary, boundary monument, and boundary reference monument positions were calculated and included in this file along the mean low water line of the Delaware - New Jersey boundary. These values were calculated from descriptions in the 1934/1935 U.S. Supreme Court Decree.


Spatial Reference System(s)
NAD83 Delaware State Planre Meters (EPSG:26957, EPSG:2776, or ESRI:102257 should all work fine)

Use Constraints

Please give proper credit to the Delaware Geological Survey.

Additional Notes

These datasets were produced to serve as a representation of the Delaware State boundary and land outline in support of the Delaware's Spatial Data Framework/DataMIL project.

Official State Boundary
Mr. William Schenck of the Delaware Geological Survey graciously provided most of the sources that were used either directly or indirecly to create this version of the lines comprising the Delaware State boundary. A text file containing NAD83 (1991) point positions for boundary and reference monuments was created. This information was extracted from Joint Agreements between the States of Delaware, New Jersey, Pennsylvania, and Maryland. Not used were computed boundary points and boundary reference monument positions from "Exhibit C" of the Joint Agreement between Delaware and New Jersey along the 1934 mean low water line (20010829). Added to this text file were 1) additional calculated positions along the Delaware - New Jersey boundary originating from the 1934/1935 U.S. Supreme Court Decree, and 2) other pertinent miscellaneous point positions used in the computation and delineation of the boundary. The mean low water line portion of the boundary between the States of Delaware and New Jersey was revised by locally registering the composite map from the 1934/1935 U.S. Supreme Court Decree with the USGS boundary DLG data and the 2002 orthoimage. The geometry of this revised boundary was then registered to the calculated positions of appropriate monuments as described in the 1934/1935 U.S. Supreme Court Decree. A series of GIS computer software (ESRI Arc Macro Language) - AML) programs were developed by Mr. George Miller of the USGS that used as input, the positional data from the source information listed above. Output from this program yielded an an ESRI coverage. The ESRI coverage data were then exported to point, line, and polygon shapefiles. The line shapefile was then interactively edited in order to fulfill specific content and attribution requirements.

State Outline
The Delaware State Outline GIS dataset comprises the bounding lines relating to the official political boundary delineation for the State of Delaware (described above) as well as the shoreline digitized from the 0.25-meter resolution 2002 orthophotos of Delaware.

In creating the state_coastline shape file close attention was paid to the natural shoreline. Man-made modifications were taken into account where need be if they protruded from the shoreline and appeared to be of solid composition (i.e. stone/poured concrete structures resting on solid ground; no floating or wooden structures were included in the outline). Man-made embayments, channels cut into the previously existing shoreline maintained by the use of bulkheads or by other means, were not taken into account; the line was drawn across the openings for such features. The same course of action was taken in the case of the mouths of rivers', as such features are not true components of the shoreline itself. In general, the line was drawn to fit what appears to be the low-tide mark, in order to maintain consistency to the highest possible degree. For this reason the line may appear to fall into the bay/ocean waters at times. In most case there is an obvious 'shoreline' (i.e. where the land ends and water starts), but in many cases there is some degree of ambiguity, and under these circumstances it was necessary to pick what appeared to be about the proper place for the line to fall. When the proper location for the line was not obvious, a point was picked that seemed to maintain the consistency of the low-tide mark. In some instances the line was drawn to include vegetation that might otherwise not be thought of as part of the shoreline. However, many of the locations upon which there is dense growth of vegetation are above water level during low-tides, and, as such, need be included within the limits of the line. The reason for the discrepancy in many portions of the line, where the water level appears different than at other points along the line, is the nature of the source photographs, i.e. their having been taken at different, seemingly random, times and therefore not necessarily coincident with times of high or low-tides.

County Boundary
A geospatial data file containing the county boundary lines as contained in fifty-four, 1:24,000-scale source boundary digital line graphs (DLGs). This data file comprises all Delaware State lands including an overedge area that extends approximately 500 feet beyond the Delaware State line. The County Boundaries for Delaware were extracted from the USGS State and County Lines layer and produced simply for deliniation of the County boundaries. This was done in 2005 by the Delaware Geological Survey for serving on the DataMIL site.