In this thesis, an ontology for the geological mapping domain is constructed using the Protégé ontology editor. The Geological Mapping ontology is developed using terms and relationships, and their properties, as they relate to creating a geologic map. This vocabulary is semantically modeled in the ontology using Web Ontology Language (OWL). The purpose of this thesis is to exemplify how an ontology can be designed and developed to represent geological knowledge as it relates to mapping.