not reflect the reality of the actual origin-destination matrix. In particular, flows with the exterior of the portion and surrounding villages are not taken into account. As a result, the BC will be able to detect important routes and nodes in the internal structure of the network but will miss large-scale communication roads such as a north-south or east-west road connecting the portion with the surroundings of Paris. In [@Strano:2012], the scale of the network was large enough so that the BC could recover important central roads such as Roman streets. The BC in the present case has then to be used as a structural probe of the network, enabling us to track the important modifications. The second point concerns the spatial distribution of the BC which will be important in the following. For a lattice the most central nodes (see the discussion in [@Barthelemy:2011] for example) are close to the barycenter of the nodes: spatial centrality and betweenness centrality are then usually strongly correlated. In [@Lammer:2006] and [@Crucitti:2006] it is shown that the most central points display interesting spatial structures which still need to be understood, but which represent an important signature of the networks’ topology.

We first consider 