# The Many Dimensions of Change in Boston, Day 4: Using Property Assessment Data to Calculate Changes in Properties’ Land Value and Floor Area Ratios

Boston recently released its annual Property Assessment data, which provides detailed information on properties in Boston. The data set can be downloaded here, and documentation describing what is in the data set is available
here.

With the release of this dataset, there are many different questions that researchers and local practitioners can pursue at different geographic scales. Here, we focus on changes in properties’ land value and floor area ratios aggregated at the census tract level.

Improvement to Land Value Ratio (ILVR):
To calculate this ratio, we divide the building value by the land value for each
parcel. Values lower than one indicate that the building value is larger than the land value, and thus, the land parcel is underutilized. We found these values for all properties in 2017 and 2018. We then calculated the percent change between the two years for each property. We aggregated these values to the census tract level by taking the mean of the changes for all properties within a census tract. The Improvement to Land Value Ratios are shown in Figure 1 below. The darker blue census tracts had at least a 10% increase in its average value; conversely, census tracts colored white indicate a decrease in its value. As we can see, there has been an increase in the ILVR over the last year in areas that are developing more rapidly (such as, South Boston, East Boston, and Hyde Park), while there was a reduction in ILVR in areas such as Roxbury and Back Bay and North End.

Figure 1: Changes in Improvement to Land Value Ratio between 2017 and 2018 in Boston

Floor Area Ratio (FAR):
The Floor Area Ratio is the total floor area of the property divided by the land area of the parcel. A FAR equal to one indicates that total floor area (including multiple levels in a building) is equal to the lot area. For example, a FAR equal to five indicates that the total floor area is five times larger than the lot area. Higher values are more common for large commercial or residential buildings that have multiple floors. We similarly calculate change in FAR as we did for ILVR. These results are shown in Figure 2 below, where darker green census tracts had larger changes in their average floor area rations between 2017 and 2018. While most of the census tracts in the city experience a no change in the Floor Area Ratio, there was an increase in several areas, such as Mission Hill, East Boston and Allston, which are areas that do not have many tall buildings. However, it is interesting to note the drop in FAR in Downtown and South Boston Area: this is a consequence of the high building density and the fact that few new buildings were added.

Figure 2: Changes in Floor Area Ratio between 2017 and 2018 in Boston

These examples illuminate different patterns of development throughout Boston. Moreover, these values can be calculate at finer geographic granularity and then linked with additional data sources available on the Boston Area Research Initiative’s Data Library. Doing so enables researchers and community leaders to pursue their specific research questions related to Boston.

Published On: April 13, 2018 |