This work is intended to provide initial considerations on building a domain ontology in the field of planetary geologic mapping and cartographic representation. It introduces formal aspects of a higher-level planetary geologic map data ontology using an OWL-based taxonomic description of objects and object properties. It is intended as a first step towards providing a common knowledge framework covering vocabularies, semantic classifications, interdependences in order to (a) build a common understanding of what planetary mappers perceive when mapping different planets and to (b) build and infer objects, properties and constraints. By establishing a focused formalism through a domain ontology, a targeted knowledge representation is created which provides means to extract and distribute information from the planetary mapping domain and allows to consistently merge map-data information retrieved from dispersed sources. Such an ontology therefore represents all knowledge aspects when dealing with planetary geologic mapping and helps to define (a) the nature and (b) the special purpose of planetary mapping in the context of geological mapping sensu lato.