The EMODnet Portal: how to present a unified data discovery and download service of complex and diverse European marine data to the public

The European Marine Observation and Data Network (EMODnet) Portal, is the service of DG Mare (Directorate-General of Maritime Affairs and Fisheries, of the European Commission) that provides public access to marine in-situ data and data products on European marine waters across the diverse subject areas of Bathymetry, Biology, Chemistry, Geology, Human Activities, Physics and Seabed Habitats.The EMODnet network is composed of subject matter experts from both the public and private sectors, that, when producing EMODnet products, collate quality controlled in-situ data and information from a number of sources, ranging from citizen science to EU member state marine observation programmes.The EMODnet Portal provides various functionalities to discover, visualise, subset and download these outputs. Furthermore, the portal and EMODnet thematics provide standard geospatial web services that can be integrated in applications and external data services.EMODnet’s backbone is a web-based network of data servers using open-source geospatial server technologies that publish services based on Open Geospatial Consortium web service standards and OPeNDAP (via the ERDDAP API) data service standards. The frontend of the EMODnet is a web-based Map Viewer connected to a GeoNetwork metadata catalogue, which provides more detailed data discovery and downloading via ERRDAP and GeoServer servers that allow subsetting and downloading of vector and gridded data.The EMODnet Portal is an operational service of DG Mare that is hosted on the European Commission’s Internet domain and therefore, since it is a public facing resource, it must be user friendly in operation, and the data being served must be delivered in a consistent manner and be well described. In addition, the Portal must also comply with the various EU laws about the Internet, e.g. web privacy and web accessibility.We present the various challenges encountered in building a consistent and accessible service. In particular, we explore the impacts of EU legislation and EC web publication rules on design decisions. and how useful the F.A.I.R principles were as a guide.