Summarizing Assessors Records

While most land parcels are owned by a single entity and assessed accordingly, there are other parcels with multiple ownership interests and separate tax assessment records. Condominiums are the most typical example—the land is held in common and each unit is assessed and taxed based on its value and share of the commonly held assets. In these cases, one parcel will have multiple associated assessor records. The “many-to-one” relation between assessor records and lot

boundaries makes it difficult to map or analyze parcel characteristics directly from the assessor data. To overcome this difficulty, MAPC summarized selected assessor’s fields for each parcel by summing the totals, finding the range, or choosing the value of one selected record. Specific methods used for each field are outlined in the table below. Some key fields are discussed here, including MAPC-calculated fields.

Assessed Values and Last Sale Date/Price

Four value fields are included in the standard assessors extract: building value, land value, other value (improvements such as swimming pools), and total value. We summed the values from the assessor records associated with each parcel. It should be noted that condominiums generally have no land value associated with individual unit records—all the value is contained within the building value for each unit. As a result, statistics utilizing land value should exclude condominium parcels. The assessor data also provides the last sale date and last sale price where it is known (the presence of this data varies widely across municipalities.) Where there were multiple assessor records for a parcel, we selected the record with the most recent sale date and use that record to populate the last sale date and last sale price for that parcel. Data are current as of the Fiscal Year indicated, and have not been adjusted for inflation. Municipalities reassess all property every three years, so the year of assessment may precede the fiscal year.

Use Codes and Building Attributes

Each assessor record includes a numeric land use code (LUC) indicating the principle use of the property. The Massachusetts Department of Revenue publishes the official list of standard 3-digit classification codes3 for use by municipal assessors. There are two challenges when attempting to summarize land use codes from the assessors extract: first, where there are multiple assessors records associated with a parcel, each could have a different LUC, and LUC values cannot simply be totaled or averaged to yield a useful summary. Second, many assessors use nonstandard codes, either a 4 digit code or a 3 digit combination not included in the DOR standard; further, the description provided in assessors data means that the same nonstandard code may indicate different land uses in two different municipalities.

To account for more than one use code is associated with a single parcel, MAPC selected both the minimum and maximum values for the LUC in each parcel. (For parcels with a single assessor record, these will be identical.) For non-standard codes MAPC applied a two-step standardization process: First, trimed four digit codes to three. Then, we matched nonstandard codes to a standard code using a manually created look-up table. The minimum and maximum values for both the “native” and standardized codes are provided in the parcel database. The “native” codes may be more useful for analysis within a given municipality, but the standard codes are essential for analyzing land uses across municipal boundaries.

Both building area and residential area values from the assessor records are summed for each parcel. Our review of records from various municipalities suggests that these fields are not consistently defined or measured by each assessor. In some cases, only one or the other field is filled in; in other cases there are values for both fields, which could be equivalent to gross and finished building area. Given this uncertainty, MAPC recommends that the most useful comparative statistic would be to take the larger of the two values (usually Building Area) and treat it as gross floor area. For the year built field, MAPC chose the most recent date.

Massachusetts Land Parcel Database-Summary

Units

Unit counts from assessor records are often absent, and/or may be unreliable. We sum the values in the “Reported Units” field but also developed our “best estimate” of unit count by analyzing two other data points: the number of assessor records reported for each parcels, and the land use code. For example, where the use code is 102 (condominiums), we estimate units based on a count of assessor records. If the unit count is absent or inconsistent with the land use code, we use the low end of the range for land use code unit count as the estimated units.

Floor Area Ratio

Floor Area Ratio (FAR) is a measure of building density. FAR is estimated using three of assessors’ data set attributes: building area, residential area, and total lot area. To resolve inconsistent definitions of floor area, we use the larger of either building area or residential area and divide by total lot area in square feet. Values over 40 (the FAR of the densest parcel observed in Downtown Boston) were assumed to be erroneous and were removed from the final dataset.

Land Cover

MAPC calculated two aspects of land cover for parcels: percent of the lot covered by a building (rooftops), and percent of the lot that is impervious but not covered by a building structure (paved area.) MAPC used MassGIS's impervious surface layer (2005) and Building Structures layer (2017) for the land cover estimates. These two estimates were combined to yield a total lot coverage estimate. Some parcels will have rooftops but no paved area if the development post-dated 2005 when the impervious surface data was collected.

Value metrics

In order to have a meaningful basis for comparing the assessed values of properties across Massachusetts towns, the values are normalized by calculating the total value per acre, building value per square foot of floor area, and land value per acre. We also estimate the ratio of building value to land value, to identify parcels with relatively high value improvements and those that may be underbuilt relative to their land value. Land value per acre, building value per square feet of floor area, and improvement/land value ratio are not calculated for condos where all value is treated as building value and land values are null.

Maintenance

MAPC plans to maintain this database with updates published by MassGIS, with data collected through our planning activities, and with spot corrections of erroneous or misleading data as necessary. MassGIS will be vigorously encouraging communities to maintain their standardized digital assessor parcel mapping in compliance with Level 3 of the digital parcel standard. Maintaining Level 3 compliant data may be no more expensive than maintaining other forms of parcel mapping. The Department of Revenue’s Bureau of Local Assessment may soon recommend that assessors maintain their mapping in compliance with Level 3 of the standard. MassGIS has assembled information and resources6 for municipalities interested in maintaining standardized parcel mapping.