This month's Atlantic explains:
"So you want to make a map," [former NASA engineer Michael] Weiss-Malik tells me as we sit down in front of a massive monitor. "There are a couple of steps. You acquire data through partners. You do a bunch of engineering on that data to get it into the right format and conflate it with other sources of data, and then you do a bunch of operations, which is what this tool is about, to hand massage the data. And out the other end pops something that is higher quality than the sum of its parts."
The sheer amount of human effort that goes into Google's maps is just mind-boggling. Every road that you see slightly askew in the top image has been hand-massaged by a human. The most telling moment for me came when we looked at couple of the several thousand user reports of problems with Google Maps that come in every day. The Geo team tries to address the majority of fixable problems within minutes. One complaint reported that Google did not show a new roundabout that had been built in a rural part of the country. The satellite imagery did not show the change, but a Street View car had recently driven down the street and its tracks showed the new road perfectly.
I've always been a map geek (which drove my Weather Now demo/application). The idea that Google will have a complete digital map of the entire world, and will presumably continue to maintain this map over the next several decades, warms my geeky heart. I wish some of this data had existed 50 years ago—or, alternately, that Google can integrate some of the existing photos and maps from earlier eras.