Nearness in space, time, or relationship. Oerlemans et al. (2001) Tijdschrift 92, 1 explain the proximity effect as benefiting from localized ties. Abramovsky and Simpson (2011) J. Econ. Geog 11, 6, 949 find evidence of co-location (within 10 km) of R&D facilities in pharmaceuticals with high research-rated chemistry departments, consistent with geographically localized knowledge spillovers and the importance of accessing academic knowledge for pharmaceutical firms.