The aim of this study is to chart the manifestation of the Chapel at Ronchamp as a plastic organism and to identify its complex intrinsic visual qualities. To use Gordon Cullen's words, the work involves ‘charting the structure of the subjective world’. Although it has graphic and figurative aspects, the Chapel at Ronchamp achieves existential meaning primarily through plasticity, in other words the visual medium of form, space, polychromy (colour as a relative phenomenon) and texture, revealed in light. As in the case of all spatially rich unicellular works of architecture, the charting of the chapel has involved about ten three-day field studies over a three-year period, recording diurnal and seasonal variations and human activity; because this is uncharted territory it has first been necessary to ‘learn’ the building. The working method has involved recording observations, accompanied by photographic sketches at fifteen minute intervals; the observations have then been correlated with a heliodon model and indicative plans and sections, including sun-paths; the character of the light admitting apertures being of particular significance. Spatial and colour relationships have then been simulated in the studio.