Here are the facts: On the evening of Feb. 26, George Zimmerman, a 28-year-old resident of the Retreat at Twin Lakes in Sanford, Fla., pursued and shot to death an unarmed black teenager named Trayvon Martin. Martin, 17, was returning to his father’s fiancée’s townhouse in the gated community after a trip to 7-Eleven, where he had purchased an Arizona iced tea and a bag of Skittles for his little brother. He was talking on his cell phone with a girlfriend.

No one questions that Zimmerman shot Martin, yet as the April issue of ARCHITECT went to press he had not been arrested. Florida’s 2005 Stand Your Ground law allows people to defend themselves with deadly force if they “reasonably believe” that they are under threat of death or extreme bodily harm in a public setting. Naturally, a lot rides on what you define as “reasonable.” The girlfriend says that Martin told her during their call that someone was following and then approached him; Zimmerman told police that he had gotten out of his car to read a sign, at which time Martin jumped him.

Meanwhile, local police face widespread accusations of botching, or even of soft-pedaling, the investigation. After weeks of growing criticism, the FBI and Justice Department have announced plans to investigate, and the state attorney general has called a grand jury hearing for April 10 to determine whether Zimmerman should be charged.

The shooting has sparked debates about race, gun control, law enforcement, and vigilantism. These are critically important issues to consider in coming to terms with what happened that night. But missing from the discussion is another potentially contributing factor: urban planning and its role in the polarization of American society.

There can be no doubt that our public discourse has become oppositional and vituperative. Social and mass media exacerbate the situation by blurring traditional distinctions between partisan commentary and objective reporting, and by creating informational ghettos where dissent is unwelcome.

Gated communities are the urbanistic equivalent of sites such as WorldNetDaily and Media Matters—places designed for homogeneity, where individuals can feel safe and avoid the unfamiliar. Yet the promise of security offered by gated communities is an illusion. Those walls and gates provide little more than product packaging and brand positioning for the developer.

In a 2010 blog postweaetxdyvaydzcwq, Kaid Benfield, director of sustainable communities at the Natural Resources Defense Council, wrote, “Subdivisions secured by gates intended to exclude outsiders may not be safer than those that are fully public. This is because they can lack the social cohesion and interaction with the larger community that for millennia have served as deterrents to crime and other antisocial behavior.”

Violence occurs in all sorts of places, for many different reasons: prejudice, greed, jealousy, desperation. The Retreat at Twin Lakes didn’t kill Trayvon Martin any more than that 9mm gun killed him—a human being pulled the trigger. But just as there is a relationship between Florida’s gun-control policies and Zimmerman’s legal possession and seeming misuse of a lethal weapon, there is a relationship between the xenophobic planning formula of gated communities and one resident’s deadly reaction to a perceived outsider.

If race was a factor, as so many argue, so too was class. Martin was traveling on foot, Zimmerman by car. A drive through a boomtown such as Phoenix or Atlanta demonstrates the obvious—that greenfield developments and even many urban redevelopments privilege the driver over the pedestrian. What’s less obvious is that such planning strategies constitute a form of discrimination. The Retreat follows this pattern: It has few sidewalks and is completely isolated from its surroundings, lacking through streets to foster physical and social connections with adjacent neighborhoods.

Many local governments have relinquished their traditional role in determining the configuration of streets. In Sanford, as elsewhere, the municipally ordained street grid is on an obscenely large scale, and developers have far too much license to fill in the blanks however they want, which usually means enclaves that turn their backs on one another and have little if anything to offer in the way of public space and other common amenities. Martin would have been less of a target had he been strolling down an active sidewalk in a cohesive neighborhood.

In our society, a car is a sign of economic prosperity, like a burgher’s protruding belly in a Dutch old master painting. Except in well-preserved older cities and some enlightened new towns, pedestrians who aren’t pushing a stroller or pulling a dog on a leash are plainly suspect—potential undesirables. In far too much of America, walking is socially taboo, logistically harrowing, and, in the case of Trayvon Martin, deadly.