Primary goal of ligand-based virtual screening is to identify active compounds consisting of a core scaffold that is not found in the current active compound pool. Scaffold-hopping is the term used for this purpose. In the present study, topological representations of pharmacophore features on chemical graphs were investigated for scaffold-hopping. Pharmacophore Graphs (PhGs), which consist of pharmacophore features as nodes and their topological distances as edges, were used as a representation of important information of compounds being active. We investigated ranking methods for prioritizing PhGs for scaffold hopping. The proposed method: NScaffold, which ranks PhGs based on the number of scaffolds covered by the PhGs, outperforms other conventional methods. As a demonstrative case, using a thrombin inhibitor data set, we interpreted the highest ranked PhGs by NScaffold from the protein-ligand interaction point of view. It resulted that the NScaffold method successfully retrieved three known important interactions, showing potential for identifying scaffold hopped compounds with interpretable PhGs.