At any one time, there are around one million people airborne somewhere in the world; that equates to an entire airborne city, a "city in the sky." Straddling whole continents, the fabric of this extraordinary construction consists of the 100,000 flights that crisscross the world every single day. Take off around the world, on the arc of an actual journey from departure to arrival, to uncover the invisible global networks and complex logistics that...