  We study the structure of a social network of strong ties (trust network)
investigating its property of connectedness versus fragmentation. To this
purpose we analyse an extensive set of census data, about marrying or having
children with immigrants, collected by Italian national statistical institute
for all Italian municipalities from 2001 to 2011. Not using neither obtaining
personal local information but only average ones, our method fully complies
with privacy and confidentiality. Our findings show that large cities display
the behaviour of highly fragmented trust networks where individuals face
possible phenomena of alienation. Smaller cities and villages instead behave
like fully connected social systems with a rich tie structure, where isolation
is rare or completely absent. While confirming classical sociological theories
on alienation in large urban areas our approach provides a quantitative method
to test them and a predictive tool for policy makers.
