Conclusion - Methods for Multilevel Analysis and Visualisation of Geographical Networks - page 204

distance, as well as the new dominating factors of speed and distance evaluation,
which creates new centres and peripheries that redistribute the concentration of
wealth and resources.

3 New Resources Throughout Networks

Network analysis provides a new perspective for spatial analysis and shifts the
focus from how many resources a location possesses to the extent to which
resources can be accessed from that location. Thus, privileged places are nodes
that access many resources through direct or indirect links and take advantage of
other nodes to reach resources they do not possess. These intermediary nodes play
new roles in the local or global network because they provide paths for accessing
resources. This strategic role implicitly introduces weaknesses into the network as
a whole. The network is fragile because reachability depends on these relay nodes
and their elimination influences the overall accessibility of the network. Although
the nodes themselves are not fragile, their position in the network and the possibility
that they might be eliminated makes those nodes fragility sites for the network. In
Sect. 3.4.3 , Gleyze noted that vulnerability occurs when the relations between nodes
are not sufficiently redundant because removing edges causes node disconnection
and the fragmentation of clusters. In relation to the issue of vulnerability, Gleyze
distinguished between n -cliques, k -plex and k -core methods.
Just as there are fragile nodes, there are also fragile edges. The network becomes
a new resource because links become more important than nodes. This feature is
important for transportation networks, where power in the network is more and more
concentrated in enterprises that manage shipping lines (see Chap. 8 )orinprimary
air traffic lines (see Chap. 9 ).
Conversely, some links or nodes are highly resilient. Robust economic and
financial edges such as the links between London and New York dominate the entire
network and connect economies in different domains. The mutual support provided
by these different networks increases their strength. Recent physical simulations
demonstrate that similar networks are more robust than different networks to the
multiple effects of failure ( Buldyrev, Parshani, Paul, Stanley, & Havlin , 2010 ;
Parshani, Rozenblat, Ietri, Ducruet, & Havlin , 2010 ).

4 Hierarchies

Hierarchies naturally appear in various contexts, and spatial geography is no
exception ( Pumain , 2006 ). The term itself may refer to an order hierarchy or a
structural hierarchy. Hierarchies may be based on organisational structure (e.g.,
NACE codes classify industrial activity into distinct sectors and subsectors) or may
emerge from territorial considerations (e.g., continents are divided into countries