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Overview
MassGIS has modified the USGS 1:24,000 Hydrography Digital Line Graph (DLG) quadrangle files to produce the Massachusetts coastline. The line feature class is named COAST25K_ARC.
Production
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. The coverages since have been projected into the Mass. State Plane Coordinate system, NAD83 meters. The individual quad coverages have been merged and dissolved.
Attributes
The TYPE (feature type) field contains the following codes:
| TYPE | DEFINITION |
| 1 | Massachusetts coastline |
| 2 | State boundary |
| 3 | Out-of-state coastline |
Editing
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.