  We studied the topology of correlation networks among 34 major currencies
using the concept of a minimal spanning tree and hierarchical tree for the full
years of 2007-2008 when major economic turbulence occurred. We used the USD (US
Dollar) and the TL (Turkish Lira) as numeraires in which the USD was the major
currency and the TL was the minor currency. We derived a hierarchical
organization and constructed minimal spanning trees (MSTs) and hierarchical
trees (HTs) for the full years of 2007, 2008 and for the 2007-2008 periods. We
performed a technique to associate a value of reliability to the links of MSTs
and HTs by using bootstrap replicas of data. We also used the average linkage
cluster analysis for obtaining the hierarchical trees in the case of the TL as
the numeraire. These trees are useful tools for understanding and detecting the
global structure, taxonomy and hierarchy in financial data. We illustrated how
the minimal spanning trees and their related hierarchical trees developed over
a period of time. From these trees we identified different clusters of
currencies according to their proximity and economic ties. The clustered
structure of the currencies and the key currency in each cluster were obtained
and we found that the clusters matched nicely with the geographical regions of
corresponding countries in the world such as Asia or Europe. As expected the
key currencies were generally those showing major economic activity.
