Thursday, August 8, 2013

The Haussmann Effect

A recent study by Marc Barthelemy and colleagues analyzing more than 200 years (1789–2010) of the evolution of the street network of Paris. This paper has just been added to my reading list. (via Emily Badger). By the way, Micahel Batty and his team at UCL have done a similar study analyzing the evolution of London’s street-network over a 224 year-period (1786-2010).

Barthelemy's Abstract:
Interventions of central, top-down planning are serious limitations to the possibility of modelling the dynamics of cities. An example is the city of Paris (France), which during the 19th century experienced large modifications supervised by a central authority, the ‘Haussmann period’. In this article, we report an empirical analysis of more than 200 years (1789–2010) of the evolution of the street network of Paris. We show that the usual network measures display a smooth behavior and that the most important quantitative signatures of central planning is the spatial reorganization of centrality and the modification of the block shape distribution. Such effects can only be obtained by structural modifications at a large-scale level, with the creation of new roads not constrained by the existing geometry. The evolution of a city thus seems to result from the superimposition of continuous, local growth processes and punctual changes operating at large spatial scales.

Figure 2: (a) Map of Paris in 1789 superimposed on the map of current 2010 Paris.In the whole study, we focus on the Haussmann modifications and limited ourselves to the 1789 portion of the street network. (b) Map of Haussmann modifications.
[click on the image to enlarge it]

[Image Credit: Barthelemy et al (2013)]

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