Konijnendijk’s 3–30–300 rule performs an unusually clear translation from heterogeneous evidence to an actionable urban heuristic: see three mature trees from every home; achieve roughly thirty per cent neighbourhood canopy; provide a quality green space within three hundred metres. Its intellectual importance lies less in the numerical thresholds themselves than in the attempt to coordinate three distinct dimensions of urban greenness—visibility, territorial coverage and accessible destination—within a single planning device. The rule converts an expanding evidence base on mental health, heat, air pollution, recreation and social wellbeing into a form that can circulate through municipalities and design practice. This compression inevitably sacrifices nuance, but it also reveals a crucial epistemic problem: research becomes infrastructurally consequential only when it can cross the boundary between publication and decision. The bridge to urbanism is therefore methodological as much as ecological. The paper demonstrates how scientific complexity can be transformed into a legible spatial standard while remaining open to local adaptation, equity concerns and revision.
