  In the fight against the racketeering and terrorism, knowledge about the
structure and the organization of criminal networks is of fundamental
importance for both the investigations and the development of efficient
strategies to prevent and restrain crimes. Intelligence agencies exploit
information obtained from the analysis of large amounts of heterogeneous data
deriving from various informative sources including the records of phone
traffic, the social networks, surveillance data, interview data, experiential
police data, and police intelligence files, to acquire knowledge about criminal
networks and initiate accurate and destabilizing actions. In this context,
visual representation techniques coordinate the exploration of the structure of
the network together with the metrics of social network analysis. Nevertheless,
the utility of visualization tools may become limited when the dimension and
the complexity of the system under analysis grow beyond certain terms. In this
paper we show how we employ some interactive visualization techniques to
represent criminal and terrorist networks reconstructed from phone traffic
data, namely foci, fisheye and geo-mapping network layouts. These methods allow
the exploration of the network through animated transitions among visualization
models and local enlargement techniques in order to improve the comprehension
of interesting areas. By combining the features of the various visualization
models it is possible to gain substantial enhancements with respect to classic
visualization models, often unreadable in those cases of great complexity of
the network.

Social and Information Networks;Computers and Society;Physics and Society