Network localization is an enabling technique for various wireless applications. Cooperation among nodes can provide significant coverage and accuracy improvements for location-aware networks. On the other hand, it also incurs complex coupling of position information among nodes, which hinders the understanding of the localization performance. In this paper, we develop a graph-theoretical approach to the analysis of information coupling. We show that the efficiency of cooperation for a specific node depends on the number of routes spanning from itself to the anchors, which implies that the popular sequential position estimators may be far from optimal in large networks. Our results can provide guidelines for the design of network operation techniques.