Maps are now encapsulated in the MapFragment class, an extension of Android's Fragment class. Now you can add a map as a piece of a larger Activity. With a MapFragment object, you can show a map by itself on smaller screens, such as mobile phones, or as a part of a more complex UI on larger-screen devices, such as tablets.
Because maps are encapsulated in the MapFragment class, you can implement them by extending the Android standard Activity class, rather than extending the MapActivity used in version 1.