I've recently purchased an iPhone SE and have started expermienting with turn-by-turn navigation. I've read that you can avoid using up your data plan if you chart out you trip ahead of time. The route information apparently stays in memory. Does anyone know how you would have to chart out the route in order to capture sufficient details in memory for turn-by-turn navigation? It seems to me that the latter requires quite a bit of map detail. Would you need to (for example) pan through the whole route at a particular zoom level? I'm not sure if it really matters, but I'm using voice navigation.