Densest subgraphs of a graph are determined. The graph includes vertices and edges interconnecting the vertices. Each edge connects two of the vertices and has a weight. The vertices and the edges form subgraphs from which the densest subgraphs are determined as those subgraphs having densities greater than a threshold. Clusters at levels of a hierarchy are determined based on the densest subgraphs. Each cluster includes a set of the vertices and a set of the edges of the graph. Each level corresponds to a different density of the clusters. The hierarchy is ordered from a most-dense level of the clusters to a least-dense level of the clusters.