geometrical structure of blocks (defined here as the faces of the planar street network). The effect of Haussmann modifications on the geometrical structure of blocks can be quantitatively measured by the distribution of the shape factor $\phi$ (see Methods) shown in Fig. \[fig:phi\].

We see that before the Haussmann modifications, the distribution of $\phi$ is stable and is essentially centered around $\phi=0.5$ which corresponds to rectangles. From 1888, the distribution is however much flatter showing a larger diversity of shapes. In particular, we see that for small values of $\phi<0.25$ there is an important increase of $P(\phi)$ demonstrating an abundance of elongated shapes (triangles and rectangles mostly) created by Haussmann’s works. These effects can be confirmed by observing the angle distribution of roads shown on Fig. \[fig:angles\] where we represent on a polar plot $r(\theta)=P(\theta)$ with $P(\theta)$ the probability that a road segment makes an angle $\theta$ with the horizontal line.

Before Haussmann’s modifications, the distribution has two clear peaks corresponding to perpendicular streets and in 1888 we indeed observe a more uniform distribution with a large proportion of various angles such as diagonals.

Discussion {#discussion .unnumbered}
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In this paper, we have studied the evolution of the street network 