By Joe Costa
In the 1990s, MassGIS made available a GIS coverage called BOUNDARY_POLY, which represented Massachusetts municipal boundaries without a coast as they extend into coastal waters. Massachusetts state waters extend generally to three miles beyond the coast. The three-mile boundary is reflected in the MassGIS Ocean Sanctuaries Act GIS coverage available at mass.gov/info-details/massachusetts-ocean-sanctuaries. As noted in the overview of the MassGIS TOWNSURVEY (municipal surveyed boundaries) coverage at mass.gov/info-details/massgis-data-municipalities#overview- ,
“This political boundary datalayer has been created from latitude and longitude coordinates found in the 68-volume Harbor and Lands Commission Town Boundary Atlas. This Atlas series, and updates since it was published, describes the legal boundary for each of the 351 municipalities in Massachusetts. These coordinates were recorded from surveys of the location of each boundary marker around the periphery of each community. Each survey was tied into higher order monumented survey control points. The Atlases also include detailed descriptions of each community’s boundary and location maps for each of the original boundary marker locations. The original surveys were conducted in the 1890s. The Atlas series was published in the early 1900s and has since been updated by the Survey Section of the Massachusetts Highway Department (now The Massachusetts Department of Transportation (MassDOT) – Highway Division) with changes as they are approved by the legislature.“
The municipal offshore boundaries contained in the BOUNDARY_POLY GIS coverage appear based on the information contained in the 68 atlas volumes prepared by the Commonwealth of Massachusetts, Topographical Survey Commission. Scanned downloadable versions of the atlases are available at the Massachusetts State Library’s Digital Collections Atlas collection at https://archives.lib.state.ma.us/collections/7c49a5e6-de4c-4b8c-a820-b5f5f9cc7bb8.
The BOUNDARY_POLY GIS coverage is not widely available but can be downloaded at https://buzzardsbay.org/gis-data/BOUNDARY_POLY.zip and is displayed in the interactive map below (as https://buzzardsbay.org/gis-data/BOUNDARY_POLY_BBNEP.kmz). This coverage is acceptable for general planning purposes but should not be considered definitive legal boundaries for municipal waters.