October 2008

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The Priority Habitats of Rare Species datalayer contains polygons representing the geographic extent of Habitat of state-listed rare species in Massachusetts based on observations documented within the last 25 years in the database of the Natural Heritage & Endangered Species Program (NHESP). Priority Habitat polygons are the filing trigger for project proponents, municipalities, and all others for determining whether or not a proposed project or activity must be reviewed by the NHESP for compliance with the  (MESA) and its implementing regulations. Areas delineated as Priority Habitats can include wetlands, uplands, and marine habitats—in fact, over half of the total acreage of Priority Habitat is mapped for marine habitats of state-listed rare species.  The Priority Habitats presented here are those published in the 13th Edition of the Massachusetts Natural Heritage Atlas, and are effective beginning October 1, 2008.

If your project or activity falls within Priority Habitat and does not meet a MESA filing exemption (321 CMR 10.14), then you must file directly with the NHESP pursuant to MESA. For more information, please see the Regulatory Review section of the NHESP website.

The Priority Habitats of Rare Species datalayer is stored in ArcSDE as PRIHAB_POLY.


Priority Habitats were digitized by NHESP scientists from documented observations of state-listed rare species and are based on such factors as reported species movements and known habitat requirements. The polygons were heads-up digitized in ArcView 3x, at a scale of 1:25,000, and referenced to MassGIS 2005 Color Orthos


The layer's polygon attribute table has the following fields:
PRIHAB_ID A unique identifier for each polygon. This number may be used to identify a Priority Habitat polygon when contacting the NHESP.
VERSION Indicates the effective date of the Priority Habitat polygons, as well as the edition of the Natural Heritage Atlas in which they were presented.

Displaying the Data

Priority Habitats should be displayed as follows:
  • At 1:25,000 scale or smaller (e.g. 1:35,000), as this is the scale at which the polygons were delineated.
  • Against MassGIS’s 2005 Color Orthophotos as a reference layer.
  • Using the “NHESP Priority Habitats of Rare Species” legend, which MUST accompany this datalayer on ALL maps.
  • NOTE: the following 15 towns contain Priority Habitats that are less than 1 acre in size. To effectively display these small areas, the line thickness of the polygon may need to be increased:
Barnstable Great Barrington Provincetown Sheffield
Boston Mashpee Royalston Wareham
Dartmouth Nantucket Sandwich West Tisbury
Gosnold Plymouth Scituate  


Occurrence records are continually being added, updated, deleted or otherwise modified in the NHESP database. These changes are incorporated into revisions to the Priority Habitats of Rare Species datalayer every two years and are displayed in the latest Natural Heritage Atlas.

Questions about the creation of this datalayer should be directed to NHESP at 508-389-6375.  For questions relating to the use of this datalayer in Environmental Review, please call 508-389-6380.

Also see these layers:

Last Updated 3/19/2009