March 2015


In the State 911 system as currently operating, there is a unique combination of police, fire and emergency medical (EMS) services which respond to any given location. Each unique combination of services is represented by a distinct Emergency Service Number (ESN) and linked to a set of numbered address ranges on street segments for every community in the Commonwealth in a table called the Master Street Address Guide (MSAG). The Emergency Service Zone (ESZ) polygon layer is a geographic representation of this assignment. The ESZ polygons are aggregated from tax parcel data (using the addresses found in the tax lists) and from the official town boundaries of the Commonwealth. This layer is under development in anticipation of the Next Generation 911 requirement to route calls to Public Safety Answering Points based on geographic location of the caller. It is a draft representation of the response areas for unique combinations of police, fire and emergency medical services based on the data in the MSAG. However, because of how the MSAG was constructed, the translation from tabular to geographic form is not straightforward and the assignment of many polygons needs local review. That local review is underway.


Emergency Service Zones are polygon features that represent the defined geographic service area of a unique combination of police, fire and EMS emergency responders. The process for creating these polygons was essentially a matching exercise between the MSAG and parcels for a given town. Streets names were compared and parcels were selected where the street name matched and the parcel address was within the MSAG range. Areas of ambiguity, where the parcel address did not match an MSAG range or value exactly, were assigned an ESN based on an individual evaluation. The age of the parcel data used varied by town. The polygons for the towns that have no MSAG community are identical to those in TOWNSURVEY_POLYM (multipart version of the Mass. Survey Towns, TOWNSURVEY_POLY) except where specific overlap/underlap situations have been identified. These situations occur where because of physical access or other issues, the parcel is not actually within the legally defined boundary of the responding community.

Also see the MSAG Communities data layer and learn about MassGIS' Master Address Database.


The ESZ polygons have the following fields:
TOWN NVARCHAR2(21) Official town name.
TOWN_ID NUMBER(5) Unique identifier for towns.
FIPS_STCO NUMBER(38) Unique identifier for County.
MSAG_COMM NVARCHAR2(20) Master Street Address Guide (MSAG) Community name.
ESN NUMBER(5) Emergency Service Number (ESN). Defined as a three to five digit number representing a unique combination of emergency service agencies (Law Enforcement, Fire, and Emergency Medical Service) designated to serve a specific range of addresses within a particular geographical area, or Emergency Service Zone (ESZ). The ESN facilitates selective routing and selective transfer, if required, to the appropriate PSAP and the dispatching of the proper service agency (ies).
MULT_ESN NVARCHAR2(1) Either a yes (Y) or no (N) value that describes if the TOWN contains more than one ESN per the MSAG
PARCELS NVARCHAR2(1) Either a yes (Y) or no (N) value that describes if the TOWN has digital parcel data available.
PARCEL_LEVEL NUMBER(5) The standard to which digital parcels comply. Either level 0, 2, or 3.
PSAP_ID NVARCHAR2(6) Unique identifier for a PSAP, assigned by the FCC and obtained from Verizon’s VoIP MSAG
PRIMARY_PSAP NVARCHAR2(100) PSAP name obtained from MA911.
EXISTING_REGIONAL NVARCHAR2(1) Either a yes (Y) or no (N) value that describes if PRIMARY_PSAP is associated with more than one TOWN. Used for symbology purposes.
WIRELESS_PSAP NVARCHAR2(50) The name of the State Police Barracks that would handle the wireless call from the associated ESZ.

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Last Updated 4/28/2016