Obviously, many of the economic reasons for clustering used in the literature to
explain the advantage and role of clusters do not apply to such ‘‘sub clusters,’’
agglomerated along a single street or around a few blocks area. Neither the work
force, nor the suppliers’ base, nor the customers are located in the vicinity of such
clusters. So why aren’t they spread all over the urban area in locations where
inexpensive real estate and parking would be more available? In reality, some
are—there are hundreds of Italian restaurants in Manhattan and many are the only
ones on their block; and there are many beauty salons in Boston located in suburbs
and shopping malls with few competitors within walking distance. Yet the
phenomenon of sub-clusters is evident.