Book excerpt: Map-making is a fundamental tool for developing geological knowledge. It involves data collection and interpretation and has its roots in the earliest discoveries in Earth science. It is the starting point for stratigraphic and structural interpretations, metamorphic facies, geochronology and modelling studies – and underpins civil engineering. From the beginning, geological mapping rapidly evolved into far more than being a simple spatial catalogue of observable rock types and landforms on the Earth’s land-surface: deductive reasoning allows this knowledge to infer subsurface Earth structure. However, the same approaches have also been down-scaled to deduce processes on the grain-scale; or up-scaled to look out to extraterrestrial objects. This Special Publication draws together these strands, crossing geoscience disciplines and observation scales to celebrate geological mapping, its historical importance and future directions, and its use in applied geology together with developing knowledge of Earth and planetary evolution and processes.