Here is an excellent article by TechCrunch, which goes into the immense detail & workload behind maintaining Google Maps.
Some quotes I found interesting included,
"This is where Street View is very critical. This is a simple intersection. We examine all of the intersections, determine where you can and can’t turn. Our operators jump into 3D mode, so you can see what you’re editing. Grab a no uturn sign as an “Observation”, to leave yourself breadcrumbs as you move around the system.
If there’s something that an operator can’t quite figure out, and this road is a major artery somewhere in California, they can file a ticket to send a Street View truck out again to survey the area. It’s that efficient, and that processed filled".
"As it stands, the team pushes new imagery every two weeks, 20 petabytes of it, to be exact. As the company now relies less on third-party information and imagery, it doesn’t have wait a long time to verify and push the new information. Sometimes it used to take up to eighteen months to perfect a city in the United States, but now it can be done in hours".
"Make no mistake about it, there will be a native Google Maps app for iOS 6, but it won’t be made available until it is ready to blow Apple out of the water, as this is Google’s only chance to give people a true Coke vs. Pepsi test for what they want to use to navigate the globe".
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Here's What Goes Into Making Google Maps, Will Apple Be Able To Recalculate?
http://goo.gl/40HQp