Measuring functional coherence in metropolitan regions, in particular polycentric ones, requires taking the issues of multiplexity and individual level heterogeneity more explicitly into account, as the spatial organisation of functional linkages is not necessarily identical. Based on the analysis of one type of functional linkage a region can appear to be integrated, but loosely connected based on another. We demonstrate the occurrence of multiplexity for the polycentric Dutch Randstad region, and focus particularly on the presence of individual level heterogeneity. Commuting patterns in the Randstad are strongly related to socio-demographic variables and firm characteristics largely determine the scale of buyer-supplier relationships. We present studies into functional coherence in the Randstad, and assess whether methods, including the interlocking network model, are sufficiently capable of accounting for multiplexity and individual level heterogeneity.