M2 Open Meta Data Directories

This paper presents a curated list of M2-level open data directories - platforms that do not primarily host datasets themselves, but instead aggregate and describe other open data portals. These meta-portals are valuable assets in the global open data ecosystem, as they facilitate discovery, foster interoperability, and serve as gateways to broader collections of data sources. The survey and verification of these directories was conducted in Q2/2025.