The Works

Why the ‘Wedding Cake’ Shape Matters

The “wedding cake” shape doesn’t always apply to cities that developed under non-market economies or with heavily regulated land use policies. This can affect on sprawl and commuting choices, according to a new paper focusing on Beijing.

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For Americans, the most natural city shape resembles a wedding cake. We envision tall towers rising in the city center, surrounded by a band of mid-rises and followed by decreasing density as one leaves the city. This pattern came about as a result of the market forces that shaped most Western cities, with high demand in the urban core pushing up land prices, spurring developers to make the most out of their patches of dirt by building ever-taller and denser structures.

The wedding cake shape is most obvious in cities like New York and Chicago, but it can be seen even in more “planned” cities like Paris, as researchers Alain Bertaud and Bertrand Renaud demonstrate in a paper comparing the density “gradients” of Paris and Moscow. Despite the relative lack of tall towers and a form generally limited to a pre-skyscraper, 19th-century scale, Parisian neighborhoods within five or six kilometers of the city center contain an average of 200 people per hectare, falling to below 100 people once you get around eight kilometers from the center.

In cities where government more heavily plans and directs growth, however, you see shapes other than the traditional wedding cake model. This can have profound effects on the shape of infrastructure networks and, eventually, transportation mode shares.

Bertaud and Renaud first compare Paris to Moscow, which exhibits almost the exact opposite pattern: Population densities actually grow as you leave the core, with average densities in Moscow peaking at a distance of 20 kilometers, or more than 12 miles, from the city center. Those within about 15 kilometers from downtown never reach above 200 people per hectare. The authors explain this by way of the socialist economy under which modern Moscow developed, writing:

Under Russia’s command economy, the absence of land prices removed all incentives to redevelop built-up areas. Once land was allocated, it was almost never recycled. Without price signals, it was administratively simpler to respond to current land demand pressure by developing at the periphery than to redevelop well-located areas with obsolete land uses [low density structures and industrial land]. While the city expanded outward, land use in already developed areas remained unchanged.

Following on this research, Chengri Ding, an associate professor at the University of Maryland’s National Center for Smart Growth, has undertaken a similar study of Beijing. He sketches the outline of the Chinese city’s skyline and population gradient, concluding that its planned, non-wedding cake shape has serious consequences for welfare. Valuable land goes relatively underused, Ding writes, and commuting distances are likely lengthened by significant amounts thanks to inefficient land use patterns.

Ding starts out by explaining Beijing’s peculiar shape, in which areas of restricted building heights are bounded by the city’s (in)famous concentric ring roads:

Because of a long and rich history and cultural tradition, Beijing adopts very rigid building height restrictions, particularly in central areas. For instance, building height is restricted to a maximum of 9 m. for three stories in Huangcheng, an area of 6.8 sq. km. Huangcheng areas contain the Forbidden City and Zhongnanhai that houses the office and residential buildings for the central government and officials. Maximum building height increases to 45 m. for 15 stories around the second ring [road] located about 3.5 km. from Tiananmen Square, which is defined as the city center. It further increases to 60 m. for 20 stories around the third ring of 7.5 km., and 80 m. for 25 stories between the third and fourth rings. Also, there are locational variations of maximum building height to facilitate urban air circulation. Maximum building height is 45 m. in the northwest, 60 m. in the south, and 80 m. in the east of Beijing, respectively.

Li illustrates that the planned building height increases away from the city center – Tiananmen Square. Prior to massive urban development in the first decade of the 21st century, the tall buildings are mostly concentrated in the third ring especially on the east side of Beijing. Due to the building height restrictions, Beijing is one of very few cities around the world that have an inverse density curve in the central city (rising density with distance) and an inverted U-shape curve of urban density as a whole. The inverted U-shape curve of urban density is jointly determined by planning regulations and market forces. The former dominates land development in a rising curve in the inner city whereas the latter dominates land development in a declining curve on the outskirts of Beijing. The rigid control on building height in the areas within the second ring is due to the presence of many historical and cultural sites and national security concerns. Finally, Beijing is distinguished from many other cities by its multiple ring roads that not only help to define spatial development patterns but also serve as landmarks in regulating building height restrictions.

In other words, Beijing is in part a “socialist city,” to use Bertaud and Renaud’s words, with density rising as you get farther away from downtown. But it transitions to a “market city” on the outskirts, where density falls.

Using complex mathematical analysis and economic theory, Ding finds that Beijing’s height limits increase housing prices by up to 20 percent and the geographical extent of the city — i.e., sprawl — by 12 percent. He also notes more generalized evidence for increased transportation costs as a result:

These simulations imply that the transportation impact of the [floor-area ratio] or building height restrictions can also be substantial. This is due to several reasons. First, the FAR or building height restrictions result in more land development needed to accommodate housing demand. As a result, people living in suburbs need to commute longer distances and spend more time on roads. Second, the building height restrictions reduce the intensity level of land uses and human activities.

Ding’s paper is paywalled, but was published in the January 2013 issue of Land Use Policy.

The Works is made possible with the support of the Surdna Foundation.

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Stephen J. Smith is a reporter based in New York. He has written about transportation, infrastructure and real estate for a variety of publications including New York Yimby, where he is currently an editor, Next City, City Lab and the New York Observer.

Tags: infrastructurepublic transportationinclusionary zoningthe worksparisbeijingmoscow

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