"Built-in navigational GPS" is a real possibility.
That's simply not true. GPS gets data from satellites in milliseconds. In fact, that's how GPS works: data is received from the satellites. Nanosecond timing differences are used to triangulate the position of the receiver. If GPS were "slow", it simply wouldn't be GPS.
This is how all GPS receivers work - from the sub-$100 handheld units to the stupidly expensive receivers built into high-end cars.
Fortunately, both the Touch and the iPhone have several GB of available storage on-board. It would be simple to use this for mapping data. Note that many automotive GPS units have built-in map data that is far under 1 GB in total storage.
GPS is slow to get data from satellites
That's simply not true. GPS gets data from satellites in milliseconds. In fact, that's how GPS works: data is received from the satellites. Nanosecond timing differences are used to triangulate the position of the receiver. If GPS were "slow", it simply wouldn't be GPS.
This is how all GPS receivers work - from the sub-$100 handheld units to the stupidly expensive receivers built into high-end cars.
(GPS) requires local maps on the device because it's only going to give you coordinates. They could WiFi for A-GPS, which means you have internet access. This is okay for some city usage but you are still very limited in usability.
Fortunately, both the Touch and the iPhone have several GB of available storage on-board. It would be simple to use this for mapping data. Note that many automotive GPS units have built-in map data that is far under 1 GB in total storage.