Abstract. Wayfinding in road networks is a hierarchical process. It involves a sequence of tasks, starting with route planning, continuing with the extraction of wayfinding i nstructions, and leading to the actual driving. From one task level to the next, the relevant road network becomes more detailed. How does the wayfinding process change? Building on a previous, informal hierarchical highway navigation model and on graph granulation theory, we are working toward a theory of granularity transformations for wayfinding processes. The paper shows the first results: a formal ontology of wayfinding at the planning level and an informal model of granularity mappings.