Tuesday, April 21, 2015

Two charts showing development in Boston over the decades

I've been playing around with the Assessing data from the city of Boston, here are a couple of charts to start. First, a summary by decade of the total amount of gross floor area, living area, and parcel land developed:

Second, the corresponding Floor Area Ratio (gross floor area divided by land area) of all properties built within each decade:

It's important to remember that the Assessing data only contains properties that continue to exist to this day, so anything demolished would not be recognized in this data set. I also noticed that in older properties, year of construction was sometimes rounded off to the nearest decade. And it's possible there are other errors. I had to correct a few more egregious and obvious ones (like fields being swapped), but more subtle errors could sneak by. Condos are handled by summing up the gross floor space for each unit and linking it to the land area used up by the overall building.

Without spending too much time on analysis (that's for later), I'll note that we live in a turn-of-the-twentieth century city: most of the floor space created and still existing seems to have occurred between 1890 and 1930. The 1930s and 1940s had some fairly obvious reasons for a lull, but construction never really picked back up afterwards at the same rate. My hypothesis: Zoning in its modern form was enacted in the mid-1950s, which has put a heavy damper on construction ever since.

The FAR chart shows that development generally hovered around 1.0 floor area to land area, but started to drop precipitously after 1930, until finally tanking at a miserable 0.21 during the 1960s. Although the amount of floor space developed increased from the 1950s into the 1960s, the amount of land area consumed zoomed up even higher.  Zoning could explain some of it, but it's not clear to me why the 1960s are such an outlier in terms of land area consumed. (Turns out it was MassPort's harbor holdings, at 101 million s.f., which I have cut out from the data). By the 1970s, overall floor area ratios returned to a more historically normal average of 1.0 or so. More recently, overall construction averages have exceeded 1.5 FAR, albeit using incomplete data for this decade.

For the curious reader, here is the result of summing over all the parcels in the database:

  • Boston parcels gross area: 651,202,719 s.f.
  • Boston parcels land area: 1,268,597,774 s.f.
  • Boston parcels FAR: 0.51


  1. Could the 1960s land consumption be explained by Urban Renewal? So much of the West End and other areas being demolished and built on, but so little of it residential?

    1. I thought about that. Demolition took place in ~1959, I suppose the buildings constructed would be considered 1960s. But even though those high-rise projects were very wasteful of land, I don't think they were THAT wasteful. I haven't had a chance to more closely examine the parcels in question yet.

  2. I can't figure out the difference from the chart between gross floor area, living area and land area. Gross floor area seems to be the total amount of built space, living area the residential space and then what's the third?

    If it includes all development, including things like highways and parks, then I think you have your answer: the Mass Pike expansion, the Central Artery, the Southeast Expressway, Logan Airport expansion and urban renewal. Plus the outermost neighborhoods, like Roslindale, West Roxbury, Hyde Park and even parts of Brighton have much bigger lot sizes - which would be thanks to zoning.

    1. Land area is 'land'. Not sure how better to explain that one.

      FAR = gross floor area divided by land area.

      No, it does not include highways and parks. This is parcel data, so it only includes the land on which parcels exist.

      Larger lot sizes wouldn't explain why the enormous bump is in the 1960s because much of those areas were developed prior to the 1960s.

      However, I did isolate the blip in the data in this case, and it's caused by MassPort, which has along the East Boston Harbor waterfront a basically undeveloped 101 million square foot piece of land that was listed as being 'built' in 1960.


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