Case Studies Atlas of Local Sustainability Transition (CASTAL): Lessons learned in building a tool for Open Science and decision-making

This article presents the conceptual foundations, operational methodologies, technical architecture, and long-term sustainability framework of the Case Studies Atlas of Local Sustainability Transition (CASTAL). Funded under the European Open Science Cloud (EOSC) through the OSCARS framework, CASTAL establishes a FAIR-compliant Atlas that ingests, standardises, enriches, and archives over 500 European Local Sustainability Transition (LST) case studies within the Social Sciences and Humanities (SSH) domain. The paper details the data harvesting and curation pipelines, the integration with DASSI and CESSDA ERIC infrastructures, and the practical utility of the archive through ten secondary studies conducted by early-career European researchers. It also synthesises lessons learned regarding Open Science operationalisation in SSH, community-driven updating workflows, and decision-support systems for decision-makers.