HERE is a video from Nokia that talks about how quality HERE Maps are created. It is not that easy to create a quality map after all!!
HERE maps aren’t magically created in a computer, though that is certainly a part of the journey. The information comes from a variety of sources. From satellites and from planes initially, but in some ways, this is the lowest resolution of map we deal with. From HERE mapping vehicles, collecting 700,000 points a second to pick up every nuance of city streets in three dimensions. We acquire open data and other official sources. And then, of course, there are the members of our HERE Map Creator communities, extending our reach and rapidly adding local knowledge.