Being able to move independently is a skill that seems necessary for social inclusion and participation. However, people with intellectual disabilities often face difficulties in developing autonomous mobility. Similarly, existing mobile navigation aid systems, which could help them to move from one place to another, are not adapted to their cognitive specificities. The purpose of this paper is to present an ontology of spatial navigation established to serve as a basis for the development of mobility aid systems adapted to people presenting an intellectual disability. It presents the method used to create the ontology, a representative extract of the ontology obtained and an illustration of the use of the ontology for the development of a mobility aid system. The limitations of the ontology and future work are also discussed.