>>1024521 (OP)
>>1024573
>100 drones per city
So here's the problem: a delivery truck can deliver hundreds of packages a day. Sure, in an urban environment the delivery truck will take longer to get there than the drone, however, it is far more efficient. Whereas the drone charges, leaves the DC, delivers to the address, and then returns to the DC to spend 30-120 minutes charging, the delivery truck can make trip after trip, delivering package after package, on a single tank of gas. Furthermore, let's say 100 drones were making deliveries all day, which took on average ten minutes to get to from the DC. They then took 30 minutes to charge. That's 50 minutes a package. Let's say another ten minutes for loading-time. That's an hour. That means one drone could deliver _only_ 24 packages in a day. Now, who wants to get a package at 2am? No one! Most urban UPS drivers deliver between 9 and 4. Let's say the drones can that's only 7 packages a drone could do. All 100 of your drones would be delivering one trucks-worth of deliveries in a day.
UPS has 119k delivery "vehicles", which is everything from the big trucks to motorcycles, globally. They also only have 1,800 DCs. Yet, they're able to deliver 20 million packages and documents a day. That's an average of 168+ packages per vehicle, per day. It just doesn't make sense to use drones.
The logistics of using drones are ridiculous. Not only do you have the time and lack of volume-per-drone, but you have a major infrastructure problem. Given their limited distance, you'd have to have a DC in every single city that gets drone deliveries. That means every DC would have to have whatever the consumer is ordering. Because, if it has to get shipped from another DC, then the whole purpose of having a drone delivery is mute. Furthermore, given their limited range (remember they have to get there under load, and then return), many geographically larger cities, like LA for instance, would have to have several DCs, all with what the consumer is going to order. Think of the cost! Not to mention, to actually be effective, every DC would have to have hundreds of drones.