Research on polycentricity has focused increasingly on the multi-scalar functional organisation of polycentric urban systems. These studies have shown that the degree of functional polycentricity varies considerably across different spatial scales. Moreover, functional polycentricity is linked to two distinct concepts: spatial integration and the balanced distribution of flows. The aim of this paper is to clarify the relation between these two concepts and to highlight the implications of this conceptual distinction for empirical research across different scales. The paper examines the connectivity field method developed to measure spatial interaction in polycentric urban systems. Using detailed commuting data, the feasibility of the method in measuring both spatial integration and the balanced distribution of flows across different scales is tested in a case study from southern Finland.