The view down Martin Luther King Avenue in Southeast Washington, DC, where new businesses and residents are moving in. (Photo by Linda Davidson / The Washington Post)

Maybe you think you know a gentrifying neighborhood when you see one. It's got all the shorthand: coffee shops, new condo construction, a few old storefronts awaiting renovation.

What we think is easy to eyeball, though, is incredibly hard to identify in data. Quantitatively, what does gentrification look like? A change in median income in a neighborhood over time? In racial demographics, real estate investment, housing values, coffee shops per capita? If gentrification is the gradual displacement of working-class residents by upper-income ones, should we look at changes in the share of professional workers, or in residents with college degrees? What about shifts in the social character of a place? Can you quantify the loss of mom-and-pop corner shops in favor of national chains, or the end of cheap carry-out replaced by high-end dining?

These questions get at a fundamental problem with one of the most controversial (and fuzzy) concepts in urban policy: Even researchers don't agree on what "gentrification" means, let alone how to identify it. (And this is to say nothing of its even more problematic derivative, the "gentrifier.")

Urban theorist Richard Florida flagged a great study over at Citylab that, well, quantifies this confusion. Michael Barton, a sociologist at Louisiana State University, assessed "gentrified" neighborhoods in New York City over the last 30 years using the definitions deployed in two previous studies, a 2003 paper by Raphael Bostic and Richard Martin and a 2005 paper by Lance Freeman. Barton then compared the results to neighborhoods that have been labeled as "gentrified" by the New York Times.

All three sources fingered different parts of the city with the loaded label, illustrating two important points: Academics who don't agree on how to define gentrification won't agree on where it's happening — and the gap between their findings and the media's focus is even wider.

The Times, for example, dwelled on gentrification in neighborhoods in Manhattan and Brooklyn, like Harlem, Park Slope, and Williamsburg, making little mention of places undergoing similar transformation in other parts of the city (Barton acknowledges that this analysis is limited; other stories may have used words like "urban renewal" or "revitalization").

This map from Barton's paper contrasts Times stories from the 2000s with Bostic and Martin's method. They looked at changes over time in a suite of variables, including the proportion of white non-family households, the poverty rate and the prevalence of college degrees:

An exploration of the importance of the strategy used to identify gentrification Michael Barton
"An exploration of the importance of the strategy used to identify gentrification" in Urban Studies, Michael Barton

This map from the same decade contrasts Times coverage with Freeman's method, which tracked changes in median income, educational attainment and housing prices:

"An exploration of the importance of the strategy used to identify gentrification" in Urban Studies, Michael Barton
"An exploration of the importance of the strategy used to identify gentrification" in Urban Studies, Michael Barton

Here is Barton's takeaway:

Descriptive results show that not only was the sheer number of neighbourhoods identified by each strategy different, but also that the geographic distribution of sampled neighbourhoods varied. These are simple findings, but have potentially important implications for research that assesses the influence of gentrification on other neighbourhood outcomes such as residential displacement and crime.

The definition matters, in other words, not purely for linguistic nit-picking, but because we seldom talk about gentrification in isolation. More often, we're talking about its effects: who it displaces, what happens to those people, how crime rates, school quality or tax dollars follow as neighborhoods transform. And if we have no consistent way of identifying where "gentrification" exists, it then becomes a lot harder to say much about what it means.

This is all very academic, but there's a corollary lesson for laymen: Whatever point you're making about "gentrification" is undermined by the fact that the word has no clear, singular meaning.