The DLG quadrangles were converted into Arc/INFO coverages and projected into the Massachusetts State Plane Coordinate System. The long list of items (MAJOR1, MINOR1, MAJOR2, MINOR2...) was then concatenated to a more simplified coding system. For each feature MINORn was truncated to three characters and linked to the other minor codes to create MINOR_TOT. For example, a submerged (612) wetland (111) is now coded MINOR_TOT = 612111. The original MAJORn, MINORn pairs are no longer part of the attribute tables.

Quadrangles covering Nantucket and Martha's Vineyard were completely digitized from the 1:25,000 USGS quadrangles. Though not as thoroughly coded as the 1:25,000 DLGs, the linework is all at 1:25,000.

The scanned quadrangles were automated in-house by scanning USGS mylar separates at 500 dots per inch. The resulting images were vectorized in GRID and then edited in ARCEDIT. Features missing from the blue line separate (i.e. dams or man-made shore) were digitized from the paper quadrangles.

Four quads along the Massachusetts-Connecticut border were obtained from the Connecticut DEP and projected to the Massachusetts State Plane Coordinate System.

An ongoing project by the MassDEP GIS Program to redelineate surface water supply watersheds using digital terrain models is adding additional streams within the newly delineated watersheds. These streams are from the MassDEP Wetlands datalayer with some additional on screen digitizing from the 2005 Color OrthoPhotos. Streams added from this process are generally coded as intermittent unless field verification proves otherwise. In 2007 the outlines of all reservoirs were replaced with those from the MassDEP Wetlands datalayer so either dataset can be used with the SWP Zones datalayer. In 2008 field verified streams for the Wachusett Reservoir watershed were provided by DCR West Boylston GIS staff and added.

All of the digitized quadrangles were checkplotted at 1:25,000. The 1:25,000 DLG quadrangles were randomly checkplotted. Each of the quadrangles was edgematched to its neighboring quads. The scanned hydrography was compared both to the source mylar and to the paper quadrangles to ensure completeness.