Drone delivery works best in places where people aren't. Unmanned machines navigating through dense, populated areas are doubly disadvantaged: more people to avoid, and plenty of cheaper, faster competitors to compete with. If drone delivery becomes a thing, and plenty of companies such as Amazon are intent on making it so, it will start in places that are challenging for cars, not worth it for helicopters, and slow for people on foot or bicycles.

All signs point to drone delivery taking off first in rural areas, and according to China's state-owned news service Xinhua, Chinese online retailer JD.com is using drones for delivery.

The drones carry up to 33 pounds of cargo, over a distance of 12 miles, and at a top speed of 33 mph (24 mph in moderate rain or wind), according to JD.com's vice president, Xiao Jun, who also said the flights each cost less than a dime.