Google Maps already #1 in Apple Store, and will likely be required for many location-based apps [View all]

Less than a day after its release, Google's Maps app has become the most popular download in the iTunes store.
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Turn-by-turn navigation is included, along with traffic data, public transit times, and Street View images, which makes it considerably more complete than Apple's offering. While Nokia's maps tools are better than Apple's, the Finns still have a way to go before then can match Google's massive database.

This is going to cause Apple some problems, since the Chocolate Factory also released an iOS 6 SDK for mapping. If you're a developer looking to add mapping functions to your app, it's pretty clear that Google will be your code of choice.

The SDK is going to be the real stake through Apple Maps - it's one thing to simply offer end users another app, but the Google Maps API is so pervasive and mature I don't see developers going through the bother of a rewrite for MapKit when they can just stick with their existing Google code and tell you "download Google Maps for this app to work".