population densityCities are sacred and profane. As students of urban geography know, great density was abhorred. The masses crowded together and created a petri dish of disease. Thomas Jefferson extolled the virtues of the yeoman farmer:

He told James Madison: "I think our governments will remain virtuous for many centuries as long as they are chiefly agricultural; and this will be as long as there shall be vacant lands in any part of America. When they get plied upon one another in large cities, as in Europe, they will become corrupt as in Europe."

Jefferson disparaged the urban. In the Age of the Creative Class, great density is sacred. Jefferson's contemporary counterpoint is Jane Jacobs:

What are proper densities for city dwellings?  … Proper city dwelling densities are a matter of performance … Densities are too low, or too high, when they frustrate city diversity instead of abetting it …

Very low densities, six dwellings or fewer to the net acre, can make out well in suburbs …  Between ten and twenty dwellings to the acre yields a kind of semisuburb …

However densities of this kind ringing a city are a bad long-term bet, designed to become a grey area. …

And so, between the point where semisuburban character and function are lost, and the point at which lively diversity and public life can arise, lies a range of big-city densities that I shall call “in-between” densities.   They are fit neither for suburban life nor for city life.  They are fit, generally, for nothing but trouble …

I should judge that numerically the escape from “in-between” densities probably lies somewhere around the figure of 100 dwellings to an acre, under circumstances most congenial in all other respects to producing diversity.

As a general rule, I think 100 dwellings per acre will be found to be too low.

Jacobs turns American Exceptionalism on its head. The urbanist reverence for density is a geographic fetish, as was Jefferson's utopian ideal. Such policy thinking is density for density's sake. Tony Hsieh's magic number for innovation:

Tony Hsieh talks about his Internet juggernaut Zappos in the same way that urban planners talk about cities. In fact, the language is uncanny. He believes the best ideas – and the best form of productivity – come from "collisions," from employees caroming ideas off one another in the serendipity of constant casual contact.

This is only achievable through density, with desks pushed close together in the office, or – in the case of Hsieh’s ambitious plans to leverage the new Zappos headquarters to remake downtown Las Vegas – with company employees and community members colliding into each other on the street. For the kind of "collisionable" density he’s looking for in downtown Vegas around his company, he figures the neglected area (not to be confused with the Vegas Strip) needs at least 100 residents per acre. ...

... His evolution in thinking, he says, comes more from his earlier days as a party planner. Close one bar in the corner of a room for example, he says, and you eliminate congestion points and enable people to better flow through a party. The challenge is all about creating circulation and serendipity.

Emphasis added. Fittingly, Hsieh's density evangelism comes from a misunderstanding. How many people you pack into a room isn't important. It's all about circulation. A party with less density and better circulation is better for knowledge exchange. Isolation (i.e. corner office), not lack of density, is the problem. The redevelopment of downtown Las Vegas is based on a poorly understood metaphor.

North Korea could build the densest city in the world and it wouldn't matter:

Of the 70-odd countries I've reported from, North Korea is perhaps the most illuminating. The world's last Stalinist dictatorship is hermetically sealed from the outside world. Hardly anyone is allowed out, and hardly anyone is allowed in (it wasn't easy getting a visa.)

Because North Korea shuts out people, it shuts out ideas. That's one big reason why it is a starving backwater. Its more open cousin, South Korea, which welcomes foreigners and sends hordes of students and businesspeople abroad each year, is 17 times richer.

South Koreans worry whether their children will make it to the right university; North Koreans worry whether their children will make it to the age of five.

The central message of my book, Borderless Economics, is that when people move around, they spread new ideas, mostly for the better.

For example, the world's cheapest fridge was born of a marriage of minds between Indians in America and Indians in India. Three Indian-American engineers (Uttam Ghoshal, Himanshu Pokharna and Ayan Guha) were working on a cooling device, based on technology used to cool laptops, that they thought might work in a fridge. One of them had trained at IBM, so he knew a thing or two about computers.

While back in India visiting relatives, they decided to show their design to an Indian manufacturer called Godrej and Boyce. It so happened that Godrej was already working on a super-cheap fridge for poor rural Indians. The two teams joined forces and produced a little fridge called the Chotu Kool that will sell for a mere $70 - less than half the price of rival fridges.

The circulation of people will beat density every time. There is nothing inherently magical about cities and density. Through people, a collision of two places can happen. Such serendipity is much more likely in South Korea than North Korea, density be damned.