MassGIS - Assessors' Parcels Datalayer Description

MassGIS' Asessors' Parcels comprise a collection of digital data provided to MassGIS by individual cities and towns or regional planning agencies. The data are stored in two layers -- "Level II" parcels, which comply with the MassGIS Standard for Digital Parcels, and "Level 0" parcels, which do not meet the standard but were available in digital format.

See Status Map (PDF) for available towns.

Level II Data

The Level II digital parcel data were provided to MassGIS by communities, or their regional planning agency partners, that received parcel grants from MassGIS in 2002 and 2006. Each municipality's parcels found in this data set were provided to MassGIS separately and then appended together to form this single data layer. Most of the parcel data included in this data layer has not been updated since it was received by MassGIS in 2002/2003 and 2006.

This data layer is under development. At the present time Level II data are available for 48 municipalities.
In June 2009 parcels for Auburn were replaced with a new submission from the town representing its FY 2010 data.

The grant recipients were required to deliver digital parcel data complying with "Level II" of the MassGIS Standard for Digital Parcels and Related Data Sets. The data submitted by grant recipients were subjected to a rigorous quality assurance process to ensure compliance with the standard. The standard establishes requirements for how parcel boundaries are compiled. It also requires establishing a few attributes of the polygons that are unique to the standard. In addition, the standard requires that a minimum selection of information from the assessor's database be included in a separate database table that can be linked to the parcel polygons. At Level II of the standard, an "intersection table" is required, which makes it possible to correctly model the one-to-many and many-to-many relationships that exist between assessor map polygons and assessor databases.

In ArcSDE, MassGIS stores the polygons as ASSESSPAR_POLY. The intersection table is named ASSESSPAR_POLY_INT and the database table is named ASSESSPAR_POLY_DATA. Two relationship classes have been built to link the polygons to the database table, by way of the intersection table: ASSESSPAR_POLY_REL1_POLY2INT relates the polygon layer to the INT table on LOC_ID, and ASSESSPAR_POLY_REL2_INT2DATA relates the INT table to the DATA table on PROP_ID. Data distributed to the publc is stored in a spatial view named ASSESSPAR_POLY_PUBLIC.

Compliance with Level II of the Standard

Users of parcel data that MassGIS has approved as meeting the requirements for Level II of its standard may find places where the boundaries conflict with visible features on orthophotos. MassGIS' QA process is not perfect. It is possible that we might miss some boundary compilation errors. However, it also very likely that a discrepancy is real. The largest source of discrepancies are disagreements between how road rights-of-way are built as compared to how they are depicted on assessor maps; this applies both to right-of-way widths and to road confgiuration. In this context, one community in particular requires special mention.

In reviewing the Town of Auburn's parcel data for compliance with Level II, MassGIS found a few areas of the town where the discrepancies between the assessor boundaries and the orthophoto were widespread and very noticeable. After consulting with the town's contractor and the assessor, and after reviewing scans of selected assessor maps and a few plans from the Worcester Registry of Deeds, we found that the construction of roads and houses in these portions of the town did not agree with the original approved plans. Also, sometimes the quality of the approved plans was sub-standard. In other words, in parts of Auburn, the digital parcel mapping is a correct rendition of the assessor's maps but the assessor's maps were sometimes updated from sub-standard plans and/or development did not match the approved plans. The town is in the process of identifying areas that will need to be redrawn where there are surveys available that indicate errors in the existing mapping.

Level 0 Data

In addition to acquiring Level II data, MassGIS has been collecting "non-Level II-compliant" digital parcel data from other communties. The quality of these "Level 0" data is very uneven and, for any given community, the data may not represent a current version of the assessor's parcel mapping.

In ArcSDE, MassGIS stores the polygons as ASSESSPARNC_POLY. Data distributed to the publc is stored in a spatial view named ASSESSPARNC_POLY_PUBLIC.

Level 0 data are available for 150 municipalities.
In June 2009 data were added for Amesbury, Millbury, Southborough and Watertown; data were replaced for Ashland, Bourne, Dennis, Orleans, Provincetown, Truro, Wellfleet and Yarmouth.