D4.2: Guidelines for citizen science data interoperability

This deliverable (D4.2) provides practical, operational guidelines for achieving interoperability and FAIR alignment in citizen science data so that it can be effectively connected, discovered and reused across European research, policy, and mission-oriented infrastructures. Building on the repository analysis conducted in D4.1 and the broader CROPS objective of supporting the upscaling of citizen science to the ERA level, this report translates conceptual interoperability requirements into concrete steps that practitioners can implement throughout the data lifecycle. Citizen science already demonstrates strong potential to complement institutional datasets across the EU Missions; however, D4.1 highlighted persistent challenges that inhibit systematic reuse, such as inconsistent metadata, unclear licensing, heterogeneous formats, and limited pathways into mission-specific repositories. D4.2 responds directly to these gaps by providing a structured approach to designing, managing, preparing, and publishing interoperable datasets. The guidelines consolidate best practices from European and international standards including PPSR-Core, DCAT-AP, Darwin Core, INSPIRE, ISO 19115, and EOSC recommendations. A central contribution of this deliverable is a practical, mission-agnostic interoperability checklist that helps citizen science projects make informed decisions from project planning through to publication. It emphasises four core pillars: (1) defining data and metadata requirements early, (2) maintaining methodological and structural consistency during collection, (3) documenting and validating data for reuse, and (4) selecting appropriate repositories with clear licensing and discoverability features. These principles are complemented by mission-specific data pathway analyses in Chapter 4, which illustrate how different domains intersect with European data ecosystems. Overall, the deliverable serves as an actionable reference for citizen science practitioners, data managers and researchers. It aims to increase the visibility, quality and long-term impact of citizen science data, strengthening its contribution to the Horizon Europe Missions and to broader scientific and policy ecosystems.