I may be totally wrong, but I'm pretty sure that if you have a data connection when you start your route, your route will be cached on the phone and you won't simply lose it if you go through a dead spot. The problem is that you probably need a data connection if you make a wrong turn and need course correction. But in a case like that, you'd need to cache a good deal of data if you were doing a 500 mile trip and needed all possible detours along the way. Chances are, in those cases, that at some point you'll be able to get signal back somewhere and correct your course anyway.

Frankly I don't find the feature all that useful for that reason. I find it cool, and hope that they'll let you download more info in the future, but until you can I don't see a lot of use for it, which is why I enabled it in labs ages ago but never used it. The way I see it, it's designed to give you cached info of a single place, like a city where you're going to have a data connection all the time anyway. I guess it would be better for things like touring small towns on vacation where they aren't blanketed with a data connection.


I have no idea what the experience is like on iOS, but all I can do is reiterate what Tony said: Google moved to vector mapping in their Maps app on Android (looks like it was around the end of 2010, so not quite two years ago), and I could have sworn that it wasn't long afterwards that the same thing came to the iOS version, but my research seems to tell me that it never did, which is odd. The performance increase when they made the switch was tremendous. The zooming was much more fluid and fast.