The Cultural Gems ontology turns a crowdsourced map of cultural places into a shared semantic infrastructure for European urban culture. Its central achievement is not the accumulation of more locations but the construction of an interoperable grammar through which heterogeneous institutions, municipalities and publics can describe them without erasing local specificity. Ontology engineering here becomes a form of civic design: classes, properties and alignments determine which cultural entities become visible, comparable and reusable across platforms. The work combines Linked Open Data standards with FAIR principles and competency-oriented modelling, thereby translating an existing public-facing application into a machine-actionable knowledge environment. Its conceptual importance lies in revealing that cultural identity at continental scale cannot be represented by a single narrative or taxonomy; it must be assembled through protocols capable of sustaining distributed contributions. The ontology therefore operates as both technical schema and political boundary object, coordinating plural descriptions while quietly governing the terms under which European culture enters shared digital space.
