More than ten years have now passed since Mike Goodchild wrote his seminal paper on ‘Citizens as Sensors’ (2007). Since then, Volunteered Geographic Information (VGI) has become an ever more popular research topic within the spatial sciences. Much of the VGI research in the past has focused on OpenStreetMap (OSM), which is, undoubtedly, the most successful example of VGI to date. OSM is a citizen-driven initiative to create an open map of the world, which rivals many authoritative data sets in its richness and up-to-date nature. Hence, there has been a large focus in the past on the quality of VGI and how it compares to topographic databases and other authoritative data sources. Interestingly, none of the papers in this special issue specif...