How the bullseye works
An Aztec code is read from the center outward. The concentric squares in the middle form the finder pattern, and data is laid out in layers that wrap around it. Because the scanner locates the symbol from its center, no blank margin is required around the edges.
That makes Aztec practical on crowded tickets and on phone screens, where space is tight. It was invented in 1995 by Andrew Longacre Jr. and colleagues at Welch Allyn, and it is standardized as ISO/IEC 24778.
Sizes and capacity
Aztec comes in a compact form with a smaller bullseye and a full-range form for larger payloads. Unlike QR, the amount of error correction can be chosen across a wide range, with a recommended default of about a quarter of the symbol.
- Smallest symbol: 15×15 modules (compact)
- Largest symbol: 151×151 modules (full range)
- Maximum capacity: up to 3,832 digits, 3,067 alphanumeric characters or 1,914 bytes
- Quiet zone: not required
Where Aztec codes appear
Aztec is common on rail and public transport tickets, including many printed and mobile tickets in Europe. It is also one of the symbologies allowed for airline boarding passes, alongside PDF417 and QR, and it is used on some vehicle registration and ticketing documents.