Youtuber CGP Grey is back with another deep dive into the hidden logic behind everyday systems—this time, it’s postcodes. They’re more than just extra address details; they’re the secret instructions that tell the mail how to move.

In the U.S., ZIP codes sort mail step by step through regional hubs. The UK’s alphanumeric system makes sorting easier with memorable letter codes. But Ireland threw tradition out the window, opting for a fully random system with built-in GPS precision.

Each country has its own approach—but which one is the smartest? Watch below!