Aztec Codes, PDF417 and Your Boarding Pass

Aztec codes and PDF417 are the two 2D barcodes hiding on your boarding pass, transit ticket, and driver's licence — one looks like a bullseye, the other like a stack of tiny stripes, and each was chosen for very good reasons.

Next time you fly, look closely at your boarding pass. That blocky pattern near the barcode isn't a QR code — it's usually an Aztec code or a PDF417. These formats quietly run the world of travel and identity documents, and understanding them explains a lot about why airlines and licensing offices don't just use QR everywhere. Let's decode them. 🐾

Meet the two formats

Both Aztec and PDF417 are two-dimensional barcodes, like QR and Data Matrix, but each has a distinctive look and a niche it dominates:

• PDF417 — a stacked linear code that looks like several short barcodes piled on top of each other. Standardized as ISO/IEC 15438.
• Aztec — a square code with a bullseye in the middle. Standardized as ISO/IEC 24778.

PDF417: the stacked barcode

PDF417 is the elder of the two and the odd one out in the 2D world. Rather than a true grid, it's a stack of rows, each row a little linear barcode. The name comes from its structure: each pattern (codeword) is built from 4 bars and 4 spaces spanning 17 modules — "4," "17." It reads left-to-right, row by row, a bit like reading lines of text.

Each row starts and ends with markers so a scanner can track which line it's on, which means a laser scanner sweeping across can read it even though it holds 2D-scale data. PDF417 has good capacity — enough for names, dates, document numbers, and even photos or biometric data in compressed form — which is exactly why it ended up on identity documents.

Where you'll find PDF417

• Driver's licences and ID cards — the back of many licences carries a PDF417 holding the cardholder's details.
• Boarding passes — many airlines print PDF417 on paper passes.
• Shipping and inventory labels — where a lot of data must ride along with a package.
• Postage — some mail services use it for routing data.

Aztec: the bullseye code

Aztec is the newer, more compact design, and it's instantly recognizable by the square bullseye finder pattern at its center — concentric squares radiating outward, a bit like an archery target. Data spirals around that central eye.

Aztec's signature advantage is that it needs no quiet zone — the blank margin that QR codes require around their edges. Because its finder is in the middle rather than the corners, a scanner locks onto the center and reads outward, so the code can sit right up against other printing. That space efficiency is precious on a crowded ticket. It's also robust and reads well even on low-quality screens and crumpled paper.

Where you'll find Aztec

• Airline boarding passes — especially mobile passes shown on a phone screen.
• Train and transit tickets — many rail networks use Aztec for e-tickets.
• Event tickets — where compactness and screen-scanning matter.

Aztec's center-out design and lack of a required quiet zone make it a favourite for tickets displayed on phone screens, where every millimetre counts.

Why not just use QR codes?

It's a fair question — QR codes are everywhere else. Several practical reasons explain the split:

• History and installed base. PDF417 was adopted for licences and boarding passes before QR became ubiquitous, and swapping out millions of scanners and systems is expensive. Standards, once entrenched, tend to stay.
• Scanner compatibility. Airline and rail gate scanners are often laser or specialized readers tuned for Aztec and PDF417. These formats read reliably at those gates.
• Space efficiency. Aztec's lack of a quiet zone and PDF417's flat, wide shape fit the physical layouts of tickets and card backs better than a square QR sometimes would.
• Robustness on screens and worn paper. Both formats were chosen partly because they scan dependably from a phone screen or a crumpled pass.

None of this means QR is inferior — it's just that these industries standardized on formats that suited their gates and documents, and there's little reason to change what works. For the broader family tree, see the history of 2D barcodes.

How they compare to QR and Data Matrix

Format	Standard	Look	Finder	Common use
QR code	ISO/IEC 18004	Square grid	Three corner squares	Consumer links, payments
Data Matrix	ISO/IEC 16022	Square grid	L-shape + clock track	Tiny industrial parts
PDF417	ISO/IEC 15438	Stacked rows (wide)	Row start/stop markers	IDs, boarding passes
Aztec	ISO/IEC 24778	Square	Central bullseye	Transit and airline tickets

The key contrasts: PDF417 is wide and stacked rather than square, and needs more physical width. Aztec is compact and needs no quiet zone, so it packs tightly onto small tickets. QR is the consumer generalist read by every phone, and Data Matrix is the tiny-part specialist. Our QR code vs Data Matrix guide covers that last pairing in depth.

Do they all use error correction?

Yes. Like QR, both PDF417 and Aztec use Reed–Solomon error correction, the mathematical safety net that lets a smudged or partly damaged code still be read. Aztec and PDF417 both let the issuer choose how much error correction to include, trading capacity for resilience — important when a boarding pass has been folded in a back pocket all day. Our Reed–Solomon error correction explainer covers how that works, and QR code error correction shows QR's four levels.

Can my phone read them?

Often, yes. Many modern phone cameras and barcode apps can read Aztec and PDF417, not just QR. But general phone support is less consistent than it is for QR codes, which is one reason QR remains the default for codes aimed at the general public. If you're building something for anyone to scan with any phone, QR is still the safe choice — and it's what we make.

QR Puppy's lane

We stick to standard, static QR codes because they're the universal, no-friction option for everyday use: readable by any phone, no tracking, no expiry, open source. Aztec and PDF417 are excellent at their jobs, but those jobs live in ticketing gates and licence bureaus, not on your restaurant flyer. If a plain, permanent QR code is what you need, our manifesto explains our approach, and you can create a free QR code right now.

Frequently asked questions

Is the code on my boarding pass a QR code?

Usually not. Airlines typically use Aztec codes (especially for mobile passes) or PDF417 (common on paper passes). Both are 2D barcodes like QR but were chosen for their compactness and compatibility with airline gate scanners.

Why does Aztec not need a quiet zone?

Its finder pattern is a bullseye in the center, so scanners lock onto the middle and read outward rather than hunting for corner markers. That means the code doesn't need the blank margin a QR code requires and can sit right against other printing.

What does "PDF417" stand for?

PDF stands for Portable Data File. The "417" refers to its structure: each codeword is made of 4 bars and 4 spaces across 17 modules. It's a stacked linear barcode, essentially several short barcodes piled into rows.

Why do driver's licences use PDF417?

PDF417 holds enough data to store a cardholder's details in a machine-readable strip, and it was standardized for identity documents before QR became widespread. Its wide, flat shape also fits neatly on the back of a card.

Are Aztec and PDF417 free to use like QR?

Yes. Both are open ISO standards (ISO/IEC 24778 and ISO/IEC 15438) with no per-code fees, just like QR. The main practical hurdle is that fewer consumer devices read them out of the box compared with QR codes.