The principles of public transport network planning include coverage, frequency, legibility and directness. But trade-offs are made in implementing these principles, reflecting the economic, institutional, temporal, and natural environments in which public transport is planned, funded, and operated. Analysis of the case study of Sydney, Australia, shows how implementing network planning principles is influenced by the natural environment. The neglected influence of topography on public transport network planning can be improved through understanding of the impact of topography on planning, expansion, operations, and public transport use; measuring the nature of the walk access in providing coverage; ensuring planning guidelines recognize topography in measuring walking access; and choosing the most efficient mode topographically while ensuring other policies support multimodal networks.