OVERVIEW

MassGIS has modified the USGS 1:24,000 Hydrography Digital Line Graph (DLG) quadrangle files to produce the Massachusetts coastline. This layer is stored in the QUAD library; the layer is named COAST and each of the 84 separate coverages is named CS.

MassGIS reformatted the DLG files into Arc/INFO coverages and projected them into the Mass. State Plane Coordinate system, NAD27. The coastline was then extracted from the files and edited. Polygon topology also was created for each quadrangle.  The coverages since have been projected into the Mass. State Plane Coordinate system, NAD83 meters.

Item TYPE in each CS.AAT is coded:
 

TYPE		DEFINITION
0		Quadrangle boundary
1		Coastline
2		State boundary
9		Non-geographic feature

NOTE: Due to the complexity of the coverages, some polygons were split. The lines used to split polygons are coded 9 and represent no geographic feature.

Item TYPE in each CS.PAT is also coded:
 

TYPE		DEFINITION
1		Land
2		Water
3		Land; Represents areas outside of Massachusetts

Checkplots were produced and compared to the paper 1:25,000 quads. Some digital quads were not available from the USGS at the time of production. Those quads were manually digitized. All quads were snapped to adjacent quads to ensure a continuous coastline.

To best serve the most users, the coastline was determined to end at the first dam from the mouth of a river. In the instances where no dam was evident on the DLGs, the coastal coverage was ended 4 quadrangles in from the shore. This technique was used for the Merrimack, Neponset and Taunton Rivers.

Last Updated 3/6/2000
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