The SIM-DL theory has been developed to enable similarity measurement between concept specifications using description logics. It thus closes the gap between similarity theories from psychology and formal representation languages from the AI community, such as the Web Ontology Language (OWL). In this paper, we present the results of a human participants test which investigates the cognitive plausibility of SIM-DL, that is, how well the rankings computed by the similarity theory match human similarity judgments. For this purpose, a questionnaire on the similarity between geographic feature types from the hydrographic domain was handed out to a group of participants. We discuss the set up and the results of this test, as well as the development of the according hydrographic feature type ontology and user interface. Finally, we give an outlook on the future development of SIM-DL and further potential application areas.