By creating a highly extensible and customizable harvesting framework, metadata from diverse open data sources will be collected. Through harmonization of the harvested metadata, the gathered information can be structured and processed. Scalable analytical and visualisation methods will allow the end users to learn more about the composition of regional, national or pan-European open data repositories. For example the aggregation of catalogues of one region or country can be easily visualised to draw an exact picture of the open data situation and allow comparison to other areas. Analysing and visualising metadata will reveal hidden potential and essential insights from existing resources and identify gaps where additional open data are needed.