Residents of Boston’s Chinatown rally for protections against displacement amid new development in the neighborhood. (Photo by John Tlumacki/The Boston Globe via Getty Images)

The challenges of mapping gentrification

Cities are looking to each other for ways to identify harmful neighborhood change. But a new study cautions against a “one-size-fits-all” approach.

For all the attention paid to gentrification by urbanists — and increasingly by popular media — there’s very little consensus around the term. There’s no clear way of defining or measuring it, and there’s even wide disagreement about whether it’s good or bad. Despite conventional wisdom that gentrification is always harmful, a good deal of research finds that it doesn’t cause widespread displacement and that it can even benefit existing communities.

There’s at least one area of general agreement: cities should develop policies that mitigate any negative impacts of neighborhood change (such as evictions, displacement, or rent-burdened households) while encouraging widely beneficial forms of population growth, economic opportunity, and local investment. But to apply those policies effectively, cities need to map where harmful change is happening — and according to new research, that’s yet another case of dramatic divergence.

The study — published last week in the journal Urban Studies — comes courtesy of an MIT research team led by Benjamin Preis. The team gathered four recent maps of gentrification and displacement in major U.S. cities: Los Angeles, Philadelphia, Portland, and Seattle. Critically, each map had been developed based on very different measures of gentrification (more on that below), reflecting the general lack of consensus in this area.

Then Preis and company applied those four underlying map methods to the same city (Boston). The result was striking. There was very little overlap in terms of gentrification areas, with only seven common census tracts (out of 180 tracts in all of Boston) marked as gentrifying or “at risk” of gentrifying across the four map methods. There was also a very wide range of map coverage: the most conservative map method identified 25 at-risk tracts, while the most lenient identified 119.

The authors caution that cities could reach “very different conclusions about the location and severity of gentrification based on the method they choose.” They add:

From different variable choices to varying risk thresholds, the assumptions embedded within the methods have significant effects on what tracts are identified as vulnerable and, in turn, where city policy responses would be targeted if these methods were used.

Let’s take a closer look into why that matters.

Cities copy other cities

The four underlying maps chosen by Preis and team shared some important characteristics. The biggest was that all four had been developed by (or on behalf of) local government. That official status makes them arguably more likely to directly inform policy interventions than, say, maps produced by academics or community organizations.

Another important factor: as recent precedents in the gentrification mapping space, these maps (and the methods underlying them) would seem to be good candidates for other cities to copy. Indeed, at the time of the MIT study, Denver had directly adopted Portland’s mapping approach, while Boston had planned to adopt Seattle’s method.

That’s not too surprising. Cities share insights and innovations all the time, from ride-hail regulations to bike-share systems to High Line knockoffs. But given the global concern around gentrification, and the high likelihood that yet more cities will be looking for ways of mapping the trend, it’s essential to know whether one method is replicable in another place.

In other words, if different mapping methods lead to wildly different conclusions about the geography of gentrification — as this study suggests they do — then any new map based on those methods might not be reliable. That could lead to inefficient or ineffective policy interventions, channeling limited resources to the wrong places.

At the core of this map gap is the selection of factors used to measure harmful neighborhood change. In the case of the four maps reviewed for this study, these factors included measures of non-white, college-educated, and rent-burdened populations; statistics around average household income, rental cost, and housing prices; and the ratio of low-to-high income households.

But the specific factors varied widely by map method, based largely on what each effort determined to be a clear cause or sign of gentrification. As the researchers note:

The variables included in or excluded from the different methods relate at the most fundamental level to their authors’ decisions about the most salient causes and indicators of gentrification, highlighting the degree to which they understand gentrification to be driven by private investment, rent gaps, state-led public investment or changing consumer preferences towards city living, to give a few examples.

I’ve shared a bit more on each method in the bullets below, but it’s worth noting that far more detail is available in the full paper. (It’s also worth noting that the study itself didn’t aim to evaluate the validity of each method.)

Los Angeles. The city’s “innovation team” developed an Index of Displacement Pressure that mapped neighborhoods by two scores: the first used six factors to identify neighborhood change, and the second used seven different factors to identify displacement pressures. Key factors included rental and housing costs, race, availability of affordable housing, and proximity to public transit.

The city’s “innovation team” developed an Index of Displacement Pressure that mapped neighborhoods by two scores: the first used six factors to identify neighborhood change, and the second used seven different factors to identify displacement pressures. Key factors included rental and housing costs, race, availability of affordable housing, and proximity to public transit. Philadelphia. The Philadelphia Federal Reserve produced a study of neighborhood gentrification that included a section meant to guide practitioners and city officials. The approach focused strictly on the rent gap, excluding factors such as race as well as public investments such as transit, and instead focusing on changes in household income, education attainment, and housing (or rental) costs.

The Philadelphia Federal Reserve produced a study of neighborhood gentrification that included a section meant to guide practitioners and city officials. The approach focused strictly on the rent gap, excluding factors such as race as well as public investments such as transit, and instead focusing on changes in household income, education attainment, and housing (or rental) costs. Portland. The city commissioned a Gentrification and Displacement Study developed by Portland State housing scholar Lisa Bates. The approach focused on housing markets and private investment (factors included housing price, proximity to affluent areas, and household income, but not public transit), laddering up to three key dimensions: vulnerability to displacement, demographic change, and housing market appreciation.

The city commissioned a Gentrification and Displacement Study developed by Portland State housing scholar Lisa Bates. The approach focused on housing markets and private investment (factors included housing price, proximity to affluent areas, and household income, but not public transit), laddering up to three key dimensions: vulnerability to displacement, demographic change, and housing market appreciation. Seattle. The city’s 2035 Comprehensive Plan mapped potential gentrification and displacement based on 14 variables, mapping a total “Displacement Risk” score. The approach focused on rent price and development potential, with key variables including measurements of income, race, and rent-burden, as well as a very wide range of neighborhood amenities, such as transit, businesses, and job proximity.

Different measures, different maps

If the different mapping approaches were equally reliable, then the four Boston maps should have identified more or less the same neighborhoods as being at risk of (or already experiencing) gentrification. Suffice it to say, the four maps were not more or less the same, with the four methods producing what the researchers call “very different maps of gentrification-related displacement risk.” That much is clear from maps of the four methods shown side by side: