Luckily each unit has a number that indicates the floor and each floor probably has a floormap near the elevator, so you won’t have to go knocking on random doors until you find the person.

Same thing for making deliveries in cities of several million. If there’s an effective addressing system, it’s usually trivial to find the destination, or at least to get very close to it and switch to “ok wtf is going on here with the last bit of this address?” mode.