This is a feature that I wish every mapping application had. When I had a Nexus 7, the Google Maps app on Android had a great feature that allowed you to save offline maps. Since the Nexus 7 had a GPS, even without a cellular data plan, you could navigate with the Google Maps app (though getting directions was not available).
Now, Gizmodo reports that a similar feature is available on the new Google Maps 2.0 for iOS. Though it doesn't have the GUI elements that show you what maps you have saved, and it isn't a very obvious feature, it's simple enough to use.
... just type in the phrase 'ok maps' (a riff off of Google Glass' OK Glass) into the search bar and search for it. Google Maps will automatically download all the map data that's currently on the screen of your phone.
I'm pretty happy about this because it means that maybe I won't have to rely on apps such as MotionX GPS. I'm not sure how long the data stays downloaded. Hopefully, this feature gets an added GUI element so that there is some sort of assurance that the map data is still there, or if I want to delete some specific map data. Currently, it's only possible to delete all map cache data, as a comment on the Gizmodo article indicates:
Open Google Maps and slide over to Settings, then go to "About, terms, & privacy". Tap on "Terms & Privacy" then tap on "Clear application data" to remove all local map caches.