Castellar and colleagues address the conceptual instability that accompanies the rapid institutionalisation of nature-based solutions. Their iconic contribution is a common classificatory architecture: thirty-two interventions are consolidated and organised through categories capable of distinguishing stand-alone units from broader systems and strategies. The theoretical advance lies in showing that terminology is not secondary to implementation. Without shared distinctions, heterogeneous projects cannot be compared, assessed or mainstreamed across policy environments. Methodologically, the study combines elicitation workshops, web-based surveys, hierarchical clustering, qualitative performance scoring, principal component analysis and evenness measures across four European projects. Its conceptual operation is infrastructural classification: naming establishes an interoperable field through which ecosystem services and urban challenges can be aligned without erasing functional difference. The wider bridge reaches STS, ecological engineering, policy standardisation and knowledge organisation. Classification appears here as a practical technology of coordination, capable of enabling transdisciplinary action while simultaneously determining which forms of urban nature become institutionally recognisable, fundable and reproducible.
URBANISM MEETS ART