“…This is because mobility between workplaces generates "weak" occupational ties (GRANOVETTER, 1973;AGRAWAL et al, 2006), which creates social cohesion between firms exchanging personnel. Other work in this vein emphasizes the importance of building social capital alongside strong networks (DEFILLIPPI et al, 2006;BROWN and DUGUID, 2001) and the building of common practices for learning within different types of practitioner groups (LISSONI, 2001;WELZ, 2003). It is furthermore argued that, given the importance of fluid communication for the transfer of tacit and often highly complex knowledge, physical proximity will underline the benefits of these informal associations, hence many examples of knowledge worker ties emerge from studies of spatially clustered firms such as Silicon Valley (SAXENIAN, 1994) and the Cambridge and Munich science clusters (CASPER and MURRAY, 2005).…”