This paper analyses clusters from collaborative knowledge relations. Focusing on the interface of clusters and networks contributes to a better understanding of collaboration, within and across places and cognitive domains. We propose an empirical analysis of the Midi-Pyrenean GNSS (Global Navigation Satellite Systems) cluster. Using Social Network Analysis tools we discuss the results according to (i) the structural, technological and geographical dimensions of knowledge flows, (ii) the influence of particular organizations in the structure and (iii) the heterogeneity and complementarities of their position and role..