Demographers and socio-geographers have long seen it coming but the first decade of the 21st century will be remembered as the first time more than half the people on earth, 3.3 billion of us, lived in cities.

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Demographers and socio-geographers have long seen it coming but the first decade of the 21st century will be remembered as the first time more than half the people on earth, 3.3 billion of us, lived in cities. And by 2050, according to the best projections, this figure would have risen to as many as 70 percent. As nations spend trillions accommodating these new urban dwellers, which direction should city planning take? The answer, as both Chicago and Manhattan apparently know, is up! Or is it?

As cities grow, not expand necessarily but as they gain more residents and their population density increases, researchers at the Santa Fe Institute found that urban life sped up. As cities grow, apparently their metabolisms accelerate, and doubling a city’s population may more than double its creative and economic output, a phenomenon known as “superlinear scaling!”

Shanghai: “The only way is up!” Credit: Keith Marshall, Flickr

Shanghai: “The only way is up!” Credit: Keith Marshall, Flickr

In the hyper-dense, residential skyscraper districts of Shanghai, densities can approach 125,000 people per square mile, living in “vertical suburbs” and conducting their lives indoors, living their lives between their apartments, their places of work and food courts, always seeing the same people. Despite its high density urban living, when it comes to innovation and creative impetus, however, Shanghai pales in comparison to New York, Paris, Milan and London, not to mention Silicon Valley, the Bay Area, Boston, Austin and North Carolina’s research triangle, all of which have much lower densities.

Even though a city’s innovative and creative dynamism might increase with its size, it seems that increased density of population might have the opposite effect; the degree to which people mix with each other being the most important factor for innovation and creativity. It happens in pavement-orientated London, Paris and New York, and surprisingly even in car-dependent Silicon Valley and Los Angeles. The low-density Silicon Valley manages to emulate the functions of larger, more densely populated urban areas, it seems, because its enterprising nature encourages information sharing. Packing more and more people into ever taller neighbourhoods does not on its own encourage creativity – “crude density” is what the academics Peter Gordon, of the University of Southern California, and Sanford Ikeda, of the State University of New York, call this. High-rise residential and commercial towers are not the basis of an innovative and creative metropolis.

Street-level interaction, maximizing the potential for informal contact between people in a given public space at any given time, is something that Gordon and Ikeda call “Jacob’s Density,” named in tribute to Jane Jacobs, the renowned urbanist and author of “The Death and Life of Great American Cities.” She famously said,

“In the absence of a pedestrian scale, density can be big trouble… Densities can get too high if they reach a point at which, for any reason, they begin to repress diversity instead of to stimulate it.”

The skyscrapers of Manhattan, for instance, are not its hubs of innovation but merely home to established corporate and financial headquarters, media empires and wealthy, often part-time, residents. The Big Apple’s high-tech, high-flyers are not in the high-rises but are based in mid-rise, mixed-use neighbourhoods, like the Flatiron District, Midtown South, Chelsea and TriBeCa.

TriBeCa, “mid-rise,” New York City

TriBeCa, “mid-rise,” New York City

The old Port Authority terminal building across from the Chelsea Market is Google’s New York office, for which it paid $1.8 billion in 2010 and which is second in size only to its headquarters in Silicon Valley. New York’s neighbourhoods are filled with the sort of old buildings that, in Jane Jacobs’ famous phrase, new ideas “must use.”

However, none of this is to say that New York and other world cities must be preserved and that endless (re-)use must be made of brown-field sites and old, redundant buildings. There is a move to increase density in Midtown East, for example, by raising height restrictions to 80 stories, as a means of stimulating much-needed development. There are plenty who warn against such high-rise developments, however, saying that they might not be the way forward for all cities

As reported in the Wall Street Journal by Richard Florida, director of the Martin Prosperity Institute at the University of Toronto’s Rotman School of Management and global research professor at New York University, says that balance is key:

“A great city needs a mix of neighborhoods and districts of varied heights and densities. And great care must be taken not to muck up those critical areas that spur true innovation and creativity.”

So, at the start of the 21st-century, as the majority of mankind become city-dwellers, it seems that that the late 20th-century answer to accommodating an ever-increasing population, that of high-density, high-rise living, is not the answer. In the UK, it is now generally accepted that the tower-block is a failed notion, especially when it comes to social housing, although far from all failed social housing developments were high-rise. South London’s Aylesbury Estate in the London Borough of Southwark is one of the most notorious “failed” developments in the United Kingdom and is currently being demolished prior to redevelopment of the area. It was built as a mix of high-rise, mid-rise and low-rise apartment blocks but suffered the same problems as suffered by purely high-rise developments. The Aylesbury is a vast landscape of housing and non residential development was not part of its planning, aside from a few small retail units to serve the local population.

All this suggests that well-planned, mid-rise and low-rise, mixed-use development is (probably) the answer to our growing urban populations, although lower population densities mean more urban sprawl, which itself could mean less farm land, an area that is already under pressure as more arable land is given over to fuel rather than to foodThomas Malthus‘ apocalyptic theories about population growth exceeding the land’s ability to provide food might have been negated by the advances in agriculture in the 19th and 20th centuries, but these advances will themselves be negated if the world increasingly loses farmland to low-density, mid-rise urban sprawl.

It appears that planners will need to perform an intricate balancing act, which will pit innovation, creativity and social cohesion against the need to restrict urban sprawl, the need to limit the cities’ “footprint” spreading across the world’s farmland. All this and global warming too!