SAN FRANCISCO — In a city famous for its views, the one from the observation tower of the year-old De Young Museum is among the best, stretching from the Pacific Ocean to the distant Berkeley hills.
Though most of the visitors are too busy snapping blurry cellphone pictures of the Golden Gate Bridge to notice, it's also an unusually good place to consider one of the most dramatic shifts to hit the architecture world in decades: the growing prominence of the roof -- and, perhaps more important, the top-down perspective that exposes it to view -- in the design of buildings, neighborhoods and even whole cities.
Thanks in part to the surging popularity of Google Earth and other Web-based programs, which give the public a bracingly new, if detached, way to interact with the built environment, rooftops are shedding their reputation as forgotten, wind-swept corners of the urban landscape and moving toward the center of architectural practice.
The nascent rooftop revival is visible in three very different forms from the De Young tower. Looking straight down you can see the roof of the museum's main wing, which is covered in long, thin skylights and the same copper panels that wrap the rest of the museum. Knowing it would unfurl prominently beneath the tower, the De Young's Swiss architects, Jacques Herzog and Pierre de Meuron, gave the roof extra attention.
Directly to the south is the site of the new $429-million home for the California Academy of Sciences, designed by Italian architect Renzo Piano. When it's finished in 2008, the academy will be topped by an undulating, 2.5-acre green roof, planted with wildflowers and other native species -- a remarkable piece of landscape architecture lifted 35 feet into the air.
Turning away from the windows, finally, you encounter a huge satellite photograph of San Francisco, picked specifically by Herzog and De Meuron and covering an entire wall. At the center of the image is a copper-colored speck: the museum. The photograph offers a wry twist on the idea of the observation tower in an age of digital technology and pervasive surveillance -- a reminder that while you are looking down on the world, the world is also looking down on you.
Thanks to a flurry of interest in the top-down view, architecture is full of such moments these days. Environmentally minded firms are making dramatic use of green roofs like the one Piano developed in San Francisco, which can help insulate buildings and reduce polluted storm runoff.
And in many of the world's biggest cities, increasing density means occupants of one building are more likely than ever to look down on another. The pair of towers Frank Gehry is designing on Grand Avenue in downtown Los Angeles will overlook not only new retail pavilions but also the architect's Walt Disney Concert Hall across the street.
"It's an issue in Brooklyn too," Gehry said, referring to his design for the $4.2-billion Atlantic Yards development, which will include more than a dozen tightly packed towers.
And then there's Google Earth. Using satellite images and aerial photographs, the program and its competitors, including Microsoft's Virtual Earth and Live Local, have enabled a new kind of architectural tourism, allowing Web surfers to zoom around the globe to see how buildings by Santiago Calatrava or their own houses look from above. According to Google Earth director John Hanke, more than 100 million people have downloaded the free program since its April 2005 debut.
"Our idea has been to democratize access to views of the places where people live and work," Hanke said.
The program, developed by a small Silicon Valley firm called Keyhole that Google acquired two years ago, remains a work in progress. Only a third of the world's cities are shown in high-resolution imagery, and a number, including Los Angeles, are represented by clearly outdated views. But if you view the images of a city that has been updated recently, such as London, the images are startlingly crisp.
The forgotten facade
To tour a typical American downtown with Google Earth is to see a collection of roofs that either sit forlornly empty or are littered with rusting mechanical equipment -- a lack of architectural attention that can be traced to the rise of the Modern movement a century ago. Modernist dogma, by insisting that roofs be flat, robbed urban buildings of the handsome ornament and geometric forms that grace the top of New York's Chrysler Building, L.A.'s Central Library and other landmarks.
The irony of that development is that many Modernist architects were obsessed with the roof and what to do with it. The Swiss-born architect Le Corbusier, in fact, wrote extensively about the potential of the rooftop as a building's "fifth facade."