IOS – How to show Apple Maps turn-by-turn navigation for public transport on the lock screen and Apple Watch

Without jailbreaking, the iPhone DOES cache the last few map tiles on the view, at all the view zoom levels. I'm not sure how extensive this is, and because it's only a temporary cache the data is always a second away from deletion.

Without jailbreaking, you can download an application, there are lots of them, but my favorite is called MotionX GPS, which is on the App Store. It allows you to cache and save certain types of map tiles from a variety of map modes, including Terrain, roads, and more. I'm not sure if they're specifically Google Maps, but you can get some types of maps for sure.

After jailbreaking, which is both legal and easy, you can find a couple of 3rd party utilities to help you download map tiles to the device, but most of them require you to view the tiles in the app itself, not in the Maps application.

As of right now, no, the new Maps app lacks transit directions. Instead, when you select Public Transit as your travel mode, it pops up a list of installed (or available from the App Store) apps that can provide local transit directions.

And, as of right now, no, there is no Google Maps app in the App Store (though you can still use Google Maps effectively from Mobile Safari).

There not much to do but conjecture as to why the Apple-made Maps app doesn't include transit. From Dan Moren's excellent iOS 6 review at MacWorld:

This is an odd solution for Apple, which usually prides itself on providing a consistent experience. But I suspect that handling public transit directions simply wasn’t an option for Apple at this point, and if it came down to offering a third-party experience versus no feature at all, Apple opted to not leave its users completely high-and-dry.