Research from the Association of Dutch Municipalities (VNG) reveals that only one fourth of Open Data from municipalities finds its way to the National Open Data Portal of the Netherlands. All other Open Data is published on local or regional portals solely.
A total of 42 Dutch municipalities (11% of all municipalities) published almost 2,000 datasets on the National Open Data Portal by the beginning of 2017. It largely depends on the types of local and regional administrations whether they publish their data nationally or not. In effect, mostly larger municipalities and provinces disclose their datasets on the national level besides their own portals. One can question whether the omission of data from smaller municipalities and provinces on the national portal is desirable in the light of re-using data. Broader publication by all local and provincial authorities would suit those who are using Open Data for new initiatives. The full research report on the link between local, regional and national Open Data portals is available online (in Dutch).