Scientometric techniques have been remarkably successful at mapping science but they face important difficulties when mapping research for societal problems possibly because they they are derived only from scientific documents and thus do not rely on non-academic expert knowledge. Here we aim to explore how ontologies can be used in science mapping, thus enriching current algorithmic techniques with systematic domain expert knowledge. This study introduces the methodology behind the construction of an ontology and tests potential uses in science mapping. We use obesity as a topic of case study.