Aaron Renn on ‘Generating and Preserving Diversity’

“To understand cities, we have to deal outright with combinations or mixtures of uses, not separate uses, as the essential phenomena.”

“Cities need old buildings so badly it is probably impossible for vigorous streets and districts to grow without them.”

One of Jacobs great insights was the importance of diversity and a mixture of uses to urban success.  Cities seem to be natural generators of diversity, but not universally so. Some places are lively and bustling while others remain inert. Jacobs attempted to diagnose this by identifying four key items she believed needed to be in place to actively generate diversity in an urban district:

  1. The district must serve more than one primary use, and preferably more than two.
  2. Most blocks must be short.
  3. Buildings must be mingled in their age, condition, and required economic yield.
  4. A dense concentration of people.

Some of these, such as block size, would appear to be relatively stable over time. Others respond dynamically, either bringing about or destroying diversity.  In the current “global city” era, we see two countervailing trends here, one tending to support diversity, the other to destroy it.

On the plus side, we’ve seen many formerly monolithic central business districts such as Chicago’s Loop or Downtown Manhattan see additional primary uses come into being. For example, Downtown Manhattan has seen a residential population boom. Chicago’s Loop also has vastly more residents than in years past, as well as the emergence of the so-called “Loop U”, a collection of colleges that collectively have over 60,000 students. Tourism has also taken on a more important role.

Similar trends have appeared in other cities. We see what were once 9-5 office districts or down at the heels industrial zones near the center take on several new primary uses, notably residential, educational, tourism, entertainment, and cultural hub activities.  These new primary uses bring different people, on different schedules, into the districts in question to help fuel a significant increase in liveliness and diversity.  This is exciting news for those of us who love cities.

On the other hand, we’ve also witnessed what may be a longer term threat. Jacobs also noted that diversity tended to destroy itself, particularly as one use becomes dominant and bids up rents to the point where other uses flee.  This results in a single-use office district, restaurant strip, etc.

The rise of the global city has seen outsized returns to those who participate in selected functions such as specialized finance or producer services. This has led to large cost increases in these cities which has displaced non-high end functions. Central cities are increasingly playgrounds for the rich, lacking in the diversity of people and uses that were once there.

From a Jacobsian perspective, one troubling consequence has been the reduction in the supply of older, obsolete buildings with lower economic yield requirements. Large numbers of older buildings, such as Class C office space or warehouses, have been demolished and replaced, or else converted into high end uses such as luxury condos. This is reducing the supply of lower rent buildings, undermining one of the pillars of Jacobs foundations of diversity. She noted how the hot areas tended to move around in cities as uses were displaced. So perhaps it is unsurprising that various districts in Brooklyn, for example, have become hipster and artistic havens while Manhattan has become more uniformly upscale and placid.

Whether or not these global city effects will ultimately lead to a self-undermining success is unknown. But the loss or upscale conversion of older and lower rent buildings in our central cities, while something to celebrate in many respects, should be a long term concern to those who care about truly sustainable urban diversity, especially if taken too far.

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2 comments

  1. [...] latest blog post is up over at the City Builder Book Club. It is called “Generating and Preserving Diversity.” This site is doing a study on Jane Jacobs Death and Life of Great American Cities and [...]

  2. [...] Generating and Preserving Diversity – City Builder Book Club [...]

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