WHY CITIES SUCCEED
In “Bigger Cities Do More with Less,” Luís M. A. Bettencourt and Geoffrey B. West assert that a high-rent city allows only greatly value-adding activities to be profitable, which leads to a cycle in which more talent is attracted, “pushing rents higher still, fueling the need to find yet more productive activities.” The serious downside of higher commercial property rents is that many small businesses, such as barbershops, dry cleaners and convenience stores, are forced out of residential neighborhoods. There are many services that cannot be acquired through the Internet.
Ronald Bourque
Brooklyn

Bettencourt and West seem perplexed that the San Francisco Bay Area and the Boston region outperform other, similar urban conglomerations. They attribute this to “cer­tain intangible qualities of social dynamics—rather than the development of material infrastructure.” I would suggest that although Harvard University, the Massachusetts Institute of Technology, Stanford University and the University of California, Berkeley, do instill certain intangible qualities in their students, these institutions are very much “material infrastructure” and probably explain a lot of the difference in economic development.
Lee Otterholt
Laguna Beach, Calif.

The correlation Bettencourt and West make between patents and population confuses cause and effect. Cities mostly grow because innovative companies are successful and attract employees from all over the world, not because an urban environment spurs innovation. Here in Silicon Valley most of the innovation comes from midpeninsula suburban cities between San Francisco and urban San Jose. And companies here and in Dallas strive for an informal campus style of construction with open spaces. Innovation comes from synergy among entrepreneurship, available venture capital, access to universities, a mobile and diverse workforce, and a place where people want to live.
Ben Roberts
Sunnyvale, Calif.

SUPERTALL SCRUTINY
In presenting the changes that have occurred in the design of skyscrapers since September 11, 2001, in “Castles in the Air,” Mark Lamster notes three threats: aircraft impact, earthquakes and wind. He correctly claims that structural engineers are now able to effectively design against them.

Unfortunately, the Twin Towers collapsed primarily because of fire, and nowhere in the article is fire explicitly mentioned as a structural threat. On 9/11 we clearly saw that fire can cause entire modern high-rise buildings to collapse. (Indeed, 7 World Trade Center, a steel-framed high-rise, was not struck by an aircraft but collapsed because of fire ignited by debris from the Twin Towers.) To ensure safety in ever taller buildings, the potential impacts of uncontrolled fire need to be explicitly considered during the structural design process with the same care as earthquakes and wind. While changes in escape-stair width, firefighter communications systems and the addition of sky bridges (all noted by Lamster) can only improve life safety in tall buildings, they do not prevent structural collapse resulting from fire.

Preventing another 9/11 requires that the structural engineering and architecture communities own up to the reality of what uncontrolled fire can do to tall buildings and take the necessary actions.
Luke Bisby
Senior Research Fellow in Structures and Fire
University of Edinburgh

Lamster mentions that the Bank of America Tower in New York City “creates two thirds of its own energy” with a gas generator. But it depletes our unquestionably finite supply of natural gas to generate that energy.
Bill Christian
North Bennington, Vt.

“Castles in the Air” left the false impression that high-rise buildings are inherently “green” and essential to making cities more sustainable. Compared with lower-rise con­struction, they require more energy, and their wind tunnels and long shadows diminish livability. Whereas cities do need minimum corridor and neighborhood densities to support their pedestrian and transit-based economies, an occasional high-rise barely makes a dent. Lacking definitive research on the optimal scale of a sustainable city, I’ve nonetheless made informal surveys of expert colleagues that suggest that four to 30 stories is the optimal range for buildings in a sustainable city.
Doug Farr
President, Farr Associates
Chicago

SIMPLE SECURITY
David Pogue is correct in “Password Prevented” [TechnoFiles] that our current method of making passwords is the worst of all possible worlds; it creates passwords that are nearly impossible for a human to remember but still relatively easy for a computer to guess.
The true secret to security is the reverse: a password scheme that is easy for users to remember (so they don’t write it down) but close to impossible for a computer to guess. The method of picking a string of letters and numbers gives a result that could be beaten in about three days of determined effort and is pretty much impossible to remember. A phrase of four random words, however, can be easy to remember but can require more than 500 years to guess.
Andrew Bennett
Belmont, Mass.

POVERTY PRIORITY
Edward Glaeser’s point that education matters more to the health of a city than construction and transportation projects in “Brains over Buildings” is valid but superficial. For a poor, urban community of color to prosper—or, nowadays, survive—good education that’s free and relevant is essential. But people need to eat, too.

The trouble with urban development is that the contractors and workers almost never come from the community being developed. And the article doesn’t mention the barriers erected in the past few years to accessing the two things it touts: education and entrepreneurship. Even San Francisco City College is too expensive for most people in the city’s neighborhood of Hunter’s Point, and cutbacks to faculty and classes make it futile for many. We’re all for entrepreneurship, but what about redlining, which has gotten worse and is augmented by predatory loans that are nothing but landgrabs? And try running a business without money.

Further, a metric Glaeser ignores is the rich, who have education and entrepreneurship in abundance, pushing the poor out of the cities altogether.

If the poor see that education will get them somewhere and help them feed their families, they and their kids will go for it. Otherwise, what’s the point?
Mary Ratcliff
Editor, San Francisco Bay View