Measuring Vacancy and Abandonment
Updated: Apr 5
Cities are composed of urban fabric (streets, parcels, built forms) knitted together with infrastructure (rail, ports, pipes, utilities, and so on). A set of interconnected processes, that began as early as the 1920s in certain U.S. regions, has created substantial amounts of degradation in the urban fabric, which generally takes the form of vacant land and/or abandoned buildings. These processes include the decline of industrial production in historical manufacturing towns, the shrinking share of organized labour as a total of the workforce, and housing policies that actively incentivized homeownership opportunity in the suburbs. The cities of Detroit, Philadelphia and St. Louis are prime examples of post-industrial cities that continue to deal with large amounts of vacant land.
In the U.S. there is no formal definition of vacant land that applies across the nation, and the U.S. Census does not actively collect data on vacancy or abandonment. Some definitions refer to various unused, under-used or uncultivated land; derelict land, such as land with abandoned buildings and other structures; brownfields and greenfields (Pagano and Bowman 2000). Vacant land has also different shapes and sizes, it can be fenced off or difficult to access, or un-buildable due to its morphology. It can be illegally encroached upon by households living nearby, cared for, yet technically vacant. It can be owned by private entities who are holding it, waiting for the right time to sell it or improve it. Or it can be owned by public entities, such as city agencies, state-chartered authorities, or municipal land banks. However parcels are owned, the fact that there is no clear definition of vacant land raises the issue of how to measure it.
In the case of Philadelphia, St. Louis and Detroit, even if measures of vacant land exist, the data should be taken with a grain of salt, especially when utilizing official statistics. The American Community Survey (ACS) only collects information about the occupancy status of residential buildings. This would not tell us whether a property has been abandoned, or is just temporarily without tenants. Fig. 1 illustrates what the available data from the ACS looks like in the three cities of Detroit, Philadelphia and St. Louis. A first observation is that in 2019 all three cities report a large margin of error in their vacancy rates. For instance, in Philadelphia, both numbers of occupied and vacant buildings have margin of errors of approximately +/- 2500. This should not be surprising, since neighborhoods are in constant flux and, as we will see, determining building vacancy is an effort that requires the coordination of multiple agencies and clarity/transparency of criteria.
The institutions of land banks in all three cities was an effort to evaluate the extent of vacancies with more accuracy, as well as restoring vacant buildings and land to productive use. The Philadelphia Land Bank (PLB), for instance, estimates of vacant land and vacant properties have become more readily available through the Council's open data platform (OpenDataPhilly.org), yet the Bank warns that neighborhoods are in constant flux, land changes hands, buildings are demolished, overgrown lots are reclaimed and it can take time for these changes to reflect in the data. Indeed land data is actually owned by four city departments in Philadelphia, complicating the land survey process (PLB, 2019). Philadelphia has roughly 42,100 vacant properties, of which 65% are vacant lots while 35% host vacant buildings. Taken together, those 42,100 properties amount to more than 3,000 acres of vacant property, or 5% of the City’s total developable area. Detroit's Land Bank (DLB) data is similarly parsed. According to the quarterly report for 2022, there are 76,180 vacant properties, split between 62,822 vacant lots and 13,358 hosting vacant buildings (DLBA, 2022)
Yet neither PLB nor DLB make the process of defining what vacant means and how lots or buildings become known as 'vacant' very transparent. The Land Reutilization Authority (LRA) of St. Louis, on the other hand, makes it very clear that vacancy is defined through an algorithm that incorporates indicators (see table below) from various city databases and in so doing generates a scoring card with four labels: "indeterminate", "possibly vacant", "very likely vacant" and "definitely vacant". The LRA's approach, in all its clarity and transparency, reveals a constellation of probability of vacancy that is likely occurring in Detroit and Philadelphia. We just don't get to see it at work.
Table 1. Factors determining Vacant Properties and Lots in St. Louis
The scoring is driven by the type, number and recency of services each property or lot received, which are translated into records of services. For instance, a "possibly vacant" property usually has multiple services calls by the Citizen Service Bureau because of vacancy-related issues, the number and recency of these services calls distinguishes a "possibly" from an "indeterminate" vacancy. Based on this scoring the LRA is able to breakdown vacancy by category (See Fig 2) for both lots and properties. According to 2022 data, St. Louis counts 24,458 vacant parcels, 10,395 of which are vacant properties and 14,063 are vacant lots. Of the total there's an additional 1,356 properties (932 buildings and 424 lots) which have at least one indicator of vacancy, but not enough to be included in the totals above (LRA, 2022).
Ultimately the criteria utilized by the LRA also provide a definition of abandonment as a phenomenon that becomes legible to institutions gradually, as different surveyors verify the condition of the building and/or lot, triggered by citizens' concern and complain. Yet that authorities learn about their unoccupied buildings in informal ways is not new. Already back in 2010 a survey asking city-officials in 60 cities across the U.S. to rank the mechanisms they use for learning about structure's abandonment showed that 74% of officers placed "calls from neighbors" in the top three, followed by ''informal feedback from city officials" and "tax delinquency" (Pagano and Bowman 2000). Despite the wider availability of GIS systems, which all three cities make use of to spatially understand vacancy, and now also machine learning algorithms, which only St.Louis seems to be using, understanding patterns of change in abandonment and vacancy in the city still relies on walking the land.
Detroit Land Bank Authority (DLBA) 2022 City Council Quarterly Report (Q2)
Land Reutilization Authority (LRA) 2022 Statistics for St. Louis Vacant Properties. https://www.stlvacancytools.com/stats.html
Pagano, M.A. and Bowman, A. (2000) Vacant Land in Cities: An Urban Resource. The Brooking Institute. Center on Urban & Metropolitan Policy. Washington D.C.
Philadelphia Land Bank (PLB) 2019 Strategic & Performance Report. The City of Philadelphia