This is one of those questions with a zillion possible answers. An insightful consideration of the question, however, might begin by making a critical distinction between "stopping" and "reducing." City design alone can't stop terrorism. Terror can strike any city, any time. Recent examples include Istanbul, Paris, Orlando, and Dhaka, among other cities. Terrorists often figure out new ways of breaching security barriers.

But, fortunately, there is also good news. City planning can significantly reduce terrorist threats by fostering urban conditions that diffuse or mitigate social inequity, alienation, and the "breeding ground" of radical ideologies. It doesn't hurt to reclaim some old-fashioned faith in the power of enlightened, people-centric design thinking as a bulwark against extremism.

This understanding should be at the heart of urban governance in Bangladesh, particularly in the age of global terrorism. I was in Bangladesh when the young terrorists struck Holey Artisan Bakery in Gulshan and stunned the entire nation with their savagery. I was able to visit various districts in the country after the tragedy and experience firsthand how the spectre of terrorism has permeated the whole body politic of the nation.

A government plan to crackdown on violent radicals is absolutely necessary. But it is not enough. It must dovetail with pre-emptive measures that would block the dark holes through which the young and the restless fall to become brainwashed terrorists.

Urban designers can help develop some of these measures. After all, cities have become the prime targets of terrorist attacks because people and buildings can be found here in high density and abundance. Extremists typically choose public plazas, train stations, airports, concert halls, restaurants, cinemas, schools, shopping malls, and stadiums for maximum casualty and destruction.

Shutting down all of these places, obviously, is not a good response to terror. Because, not surprisingly, without these places, the social and economic lives of cities end up on the deathbed. We need to robustly celebrate the life of the city—its entrepreneurship, its culture, its civic spirit, and its future—while also making public places secure.

The dogged optimist would think that this could be an effective way to disrupt the devious network of fanatic ideologues. One hopes life would be that simple. It is not.

One lesson to draw from the complexity of the provenance of terrorism is that the best effort to prevent it would require some proactive thinking about a range of potential causes of terrorism.

One such cause is how the city itself functions and serves or does not serve its people, fostering alienated pockets of unemployed youth, often predisposed to social anarchy and extremist ideologies. A 2013 United Nations report examined how neglecting basic principles of equitable, integrated urban planning can result in widespread social uncertainty and crime. 

Behind the shiny facade of Paris, the "city of lights," there is also what the French Prime Minister, Manuel Valls, called the "territorial, social and ethnic apartheid" of the banlieues, the dystopic suburbia of Paris, the ghettoised enclave of immigrants and their French-born children. Paris has become, as some recent observers claim, a classic tale of two antagonistic cities. One is French and the other not-quite-French. As various social analyses of the Charlie Hebdo massacre show, social alienation, fuelled by the physical isolation and despair of banlieues, can quickly morph into jihadist fantasies. The immigrant's grievance of unemployment and racial discrimination can seek refuge in violent ideologies. The Charlie Hebdo terror plot was actually born in the banlieues.

Dhaka may not have an "immigrant" problem. But it certainly has an array of urban pathologies that have the potentials to foment extremist views. Let's consider a few.

First, economic zoning. Dhaka has an entrenched elitist problem of "differential urban treatment" of people in different economic zones. Gulshan has a disproportionate concentration of urban wealth, fortified by its many local and multinational company headquarters, high-end shopping malls, Wi-Fi cafes, upper-echelon housing stock, and, recently, its own new fleet of 30 air-conditioned buses and 500 rickshaws. Gulshan is Bangladesh's epitome of self-isolating economic and social islands.

There was a perverse reason why the Holey Artisan attackers went to Gulshan. It was not just a simple case of hunting down the maximum number of foreigners or infidels. In their twisted minds, it was also about piercing the heart of Western, secular, decadent, and anti-Sharia Bangladesh with the sword of Salafist self-righteousness. It was about taking down Bangladesh's number one citadel of kaffirdom. This was the same warped logic that terrorists adopted to fly airplanes into New York's Twin Towers, the perceived architectural symbol of America's global dominance.

While Gulshan gets its own internal public transportation system, over two million workers employed in Dhaka's sprawling garment industry (accounts for 80 percent of all exports in the country) lack affordable housing, basic healthcare and education, and access to clean water and greenery. Urban policy decisions have traditionally been skewed in favour of certain economic zones over the others within the city. This asymmetry often incites antipathy among the city people who feel deprived for no good reason other than social injustice.

This should not be viewed as a clichéd restatement of the class struggle with a Marxian fury, but, really, as a question of social equity that undergirds sustainable urban planning principles that many cities around the world are increasingly adopting as a fundamental framework of urban and economic progress.

Urban planners need to think about how to integrate the city by a comprehensive system of public transportation, park system, school districts, and an equitable allocation of urban amenities. They must create one city, not fracture it into absurdly asymmetric economic zones.

Second, the city's young needs playfields to exhaust their energy. When I was growing up in Chittagong decades ago, after returning from school, my local buddies and I would eagerly wait to go to the playground in our neighbourhood. In many ways, the playground was where we grew up, became social beings, and developed our muscles.

Yes, not having Facebook and other social media then helped. But, really, how serious are urban administrators and planners in Bangladesh about preserving neighbourhood playgrounds as a way to keep the youth engaged with city life and away from the dark underworld of nefarious indoctrination? Lest we forget, about 52 out of Dhaka's 90 wards (about 60 percent of the total Dhaka metropolitan area) have no access to parks or playgrounds whatsoever. Consider this: Out of the 90 wards, only 36 have some open space ranging from only 0.01 acre to 0.21 acre per 1000 population.

Have we thought deeply about how neighbourhood playfields would help create more Shakib al-Hasans and less Nibrases?

Third, where are our urban plazas, piazzas, zócalo, malls, and maidans? Public places are where urbanites form a community. This is where the city people become the public. This is where democracy finds a voice and a physical presence. Cities in Bangladesh have been growing with unprecedented population surges. Dhaka receives nearly half-a-million rural-to-urban migrants every year. The demand for urban land is skyrocketing, unfortunately leading to misguided policies of gentrification and a mastani culture of land-grabbing.

Experts recommend that a liveable city should have a minimum of 25 percent of its total urban land area as open space. According to a 2012 study, Dhaka's open space is only about 14.5 percent and rapidly shrinking. Research has shown that without adequate public plazas—essential for a city's democratic practices, recreation, and community-building—the antisocial instincts of city dwellers balloon.

The urbanist William H. Whyte's study of pedestrian behaviour in 1960s New York is instructive. He concluded that strangers start imagining themselves as a community when they have the opportunity to freely access public plazas with others.

When community camaraderie blossoms, there is less time for jihad. And details matter. From public benches to the width of sidewalks, from pavement patterns to roadside vegetation, minute design elements provide people a sense of orientation and belonging. Although a linear cause-and-effect hopefulness would be too simple, but, as different case studies show, a strong community feeling instils more self-policing and less penchant for violence.

The Colombian city of Medellin offers a good case in point. This ungovernable city of drug warfare and assassination has lately been seen as a success story of urban regeneration. Beginning in early 2000s, three consecutive mayors heavily invested in urban plans based on public transportation, housing, and public plazas, all considered drivers of civic life and social integration. Colleagues have been encouraging me to visit Medellin to experience how a city's physical spaces can positively influence the mental world of city people.

Terrorism flourishes under various circumstances and preventing it will require a multilayered approach. Obviously, urban designers in Bangladesh alone won't be able to stop terrorist attacks in the future, but they can certainly create urban environments now that could not only effectively combat the spread of extremism, but also revitalise Bengal's cherished tradition of interfaith coexistence.

The writer is an architect, urbanist, and architectural historian. He teaches in Washington, DC, and is the author of Impossible Heights: Skyscrapers, Flight, and the Master Builder (2015) and Oculus: A Decade of Insights into Bangladeshi Affairs (2012). He can be reached at adnan_morshed@hotmail.com.