value of $a$ measured gives an estimate of the area $A\simeq 29.7km^2$, in agreement with the actual value $A=33.6km^2$ (for the 1789 portion). This agreement demonstrates that all the networks at different times are not far from a perturbed lattice.

We also plot the average route distance $d_R$ defined as the average over all pairs of nodes of the shortest route between them (see Methods for more details). For a two dimensional spatial network, we expect this quantity to scale as $d_R\sim \sqrt{N}$ and thus increases with $N$. The ratio $d_R/\sqrt{N}$ is thus better suited to measure the efficiency of the network and we observe (Fig. \[fig:general\_results\](c,f)) that it decreases with time and $N$. This result simply demonstrate that if we neglect delays at junctions, it becomes easier to navigate in the network as it gets denser.

**Typology of new links**

We can have three different types of new links depending on the number of new nodes they connect. We denote by $E_i$ ($i=1,2,3$) the number of new links appearing at time $t+1$ connecting $i$ new nodes. For example $E_0$ counts the new links appearing at time $t+1$ connecting two nodes existing at time $t$. In order to categorize more 