More broadly, authoritative data are increasingly out of date in many parts of the world (Estes and Mooneyhan, 1994), and were acquired using older technologies that were less accurate than those available to the general public today. In the US, it is easy for a volunteer to acquire data that are more accurate than the 1:24,000-scale mapping that is the most detailed complete coverage available for the continental states. Thus in many circumstances it is easy to show that VGI is of better quality than the best available authoritative data.
These arguments provide the motivation for the remainder of the paper, which addresses the question of how to assure and improve quality in VGI.