A series of MIT Media Lab maps are percolating through the internet, showing the locations and "walksheds" of independent coffee shops in San Francisco, Brooklyn, and Cambridge. These shops play an important role in urban life, as the researchers explain in their project description:

Independent coffee shops are positive markers of a living community. They function as social spaces, urban offices, and places to see the world go by. Communities are often formed by having spaces in which people can have casual interactions, and local and walkable coffee shops create those conditions, not only in the coffee shop themselves, but on the sidewalks around them. We use maps to know where these coffee shop communities exist and where, by placing new coffee shops, we can help form them.

This is all true—walkable, independent coffee shops are great!—and it's easy to imagine the sort of cute, laptop-packed establishments that the researchers are referring to. If coffee shops are a marker of a healthy community, those brightly colored communities must be healthy, and the densely packed parts must be super healthy.

Those barren neighborhoods? The researchers pretty plainly state that they could maybe use some more coffee shops, but coffee shops have, in many, many cities, been a bellwether of gentrification. In fact, an increase in coffee shops is such an excellent marker for gentrification that it's been used as a proxy for the process by researchers.

Let's take another look at those coffee shop-deprived areas. Here's the Brooklyn coffee shop map again, overlaid on the borough's racial geography, via the excellent Racial Dot Map (based on 2010 census data):

And here's the same comparison for San Francisco:

The coffee shop-less neighborhoods in these cities are predominantly non-white. If you spot a mixed neighborhood with a heavy concentration of these shops—Bushwick and Crown Heights in Brooklyn, for example—chances are it's rapidly gentrifying.

Coffee shops certainly can be "positive markers of a living community," but these maps sort of gloss over that they're really a positive marker of one fairly specific type of a living community. Informal gathering places that can make neighborhoods thrive—what urban sociologist Ray Oldenburg calls "third places"—can come in all shapes and sizes, and this diversity of communities is what makes great cities great. To one resident, a new independent coffee joint might be a welcome neighborhood amenity. To another resident—a resident who may already have a community-building space in a church, or a park, or a bar, or even a chain coffee shop—it's the gentrification equivalent of a red sniper dot.