How does a letter find its route through a postal system?

A birthday card can reach a house that its sender has never visited. The card cannot choose a road or ask for help. Its address lets many people and machines work together to carry it to the right place.

Mail is collected and sorted. Letters going toward the same area can travel together, even when they will end at different homes. Near their destination, they are sorted into smaller groups. A carrier takes each letter along the final part of its journey.

Our pretend address A2 shows how this works. A means a large region, and 2 means one stop inside it. The A letters go together first. Later, the number separates A2 from A1 and A3. If the label cannot be read, someone needs to check it.

Each helper handles part of the trip. The address stays with the envelope through every handoff, so the sender does not have to travel with the message. A little piece of paper can connect two people far apart.