Map/Navigation Apps makes my iPhone warm pretty quickly - I assume normal? What's the cause, lots of processor/graphics and of course it sucks down the battery fast too.
You got it already - anything that is processor, memory and graphics intensive will generate extra heat. Try using the hotspot feature - my 4S gets really warm with 3 other devices connected, streaming audio to my car via the dock connector AND connected hands free to my car via Bluetooth. It needs a 2.1A car charger to keep it charged.