A metropolitan green-space inventory becomes a different object when the question moves from area to reachable entrance. Pastore and colleagues integrate formal and informal green spaces with satellite and thematic spatial data, then investigate pedestrian accessibility at a 300-metre threshold. Their finding that only 37 per cent of the Milan metropolitan residential surface lies within the defined five-minute walking catchment is a statement about a carefully specified spatial relation, not a measurement of actual visits, ease of passage or experienced restoration. The paper’s contribution is to make the denominator and access criterion visible, while expanding the territory of the count beyond officially designated parks. An informal green area can exist without institutional recognition; a mapped green polygon can be nearby without offering the kind of entrance or route that everyday access requires. Urban ecology, GIS and distributive planning are therefore brought together through a deliberately operational definition of opportunity. The resulting map is powerful because it specifies one condition of possible encounter, and rigorous because it does not, by itself, certify that encounter.
