What Urban Design Reveals about Economic Development
- 2015-10-27
- Wharton
Tweaking the Circle
I work on urbanization and developing countries, and in my recent research I have looked at the spatial patterns of urbanization in India, trying to understand the economic implications of different city structures. If you look at urban areas from an airplane, for example, you can see that cities come in different shapes. Some have outlines that are roughly circular; others appear more fragmented, and yet others are constrained by their geographies. For instance, cities on islands or peninsulas end up having even more irregular shapes. My research question was what influence, if any, does a city’s shape have on the location choices of consumers and firms? Do consumers and firms benefit in terms of welfare or productivity from locating in cities with particular shapes?
Why would we expect city shape to matter at all from an economic standpoint? As urban planners have long recognized, city shape is one of the determinants of urban commuting efficiency, along with more widely studied factors, such as infrastructure or travel demand. More compact, more circular city geometries are conducive to shorter, within-city trips. To give you a sense of how this works, think of a circle. Now imagine that, holding the area constant, you start tweaking the circle, turning it into some irregular shape. As the shape of this polygon departs from that of a circle, becoming less and less compact, the average distance between points within this polygon will tend to increase. The same thing happens to cities as they expand in space.
A good, real-world example of these types of interactions is the comparison between Calcutta and Bangalore. Of the top cities in India, Calcutta is the least compact one. It kind of looks like an upside down giraffe head with a long, north-south tentacle. Bangalore, on the other hand, is more like a pentagon, and it’s the most compact one. I calculate that, all else being equal, if Calcutta had the same compact shape as Bangalore, the average within-city trip, proxied by the average distance between points within the city, would be shorter by 6.2 kilometers (3.8 miles). This is not trivial if you think that the average commuting speed in the top cities in India is around 15 kph.