Defining Polycentric Urban Areas Through Commuting Cohesion in France - Methods for Multilevel Analysis and Visualisation of Geographical Networks - page 193

Fig. 12.13 ( a ) The incoming participation coefficient around Lyon in 1999. ( b ) The outgoing
participation coefficient around Lyon in 1999

that are connected directly or indirectly with the city center grows during all of these
periods. Moreover, these municipalities become more and more geographically
distant from the city center over time.
The betweenness centrality index permits the identification of municipalities that
polarize the territory and catch workers from many surrounding municipalities. This
index illustrates the impact of the major French cities on the commuters' network.
The polycentric structure of the urban areas and its extension is also clearly
identifiable through the application of the strength index. The increasing number
of subcenters is evident, and their place and weight in the commuters' network
also grows. The number of municipalities sending commuters to these subcenters
becomes significant and increases the subcenter connectivity. More importantly, the
municipalities situated in these subcenters become more tightly connected.
Finally, by applying the participation coefficient, we can characterize two types
of municipalities: those who send workers out, defined as residential areas, and those
who receive workers, defined as employment centers.
In summary, the commuters network can be characterized by a star topology,
highlighted using the betweenness centrality index, with small world properties,
illustrated by the strength metric. In the last section of this paper, we investigate this
characterization further.

12.3.2 Creating an Egocentric Network of an Urban City

On-Demand

In this work, we extracted egocentric networks from the complete data for all four
census years to create a local view around a city of interest. The egocentric network
of a city in graph G is defined as the subgraph of G induced by the nodes of the graph
that are situated near, in a topological sense, the city of interest. The extraction is