In this paper we present an approach to the analysis of the contribution of a small subregion in a dataset to the global ﬂow. To this purpose, we subtract the potential ﬂow that is induced by the boundary of the sub-domain from the original ﬂow. Since the potential ﬂow is free of both divergence and rotation, the localized ﬂow ﬁeld retains the original features. In contrast to similar approaches, by making explicit use of the boundary ﬂow of the subregion, we manage to isolate the region-speciﬁc ﬂow that contains exactly the local contribution of the considered subdomain to the global ﬂow. In the remainder of the paper, we describe an implementation on unstructured grids in both two and three dimensions. We discuss the application of several widely used feature extraction methods on the localized ﬂow, with an emphasis on topological schemes.