Symbology
The complete specification of how a particular barcode encodes data - what characters it can carry, how the bars are drawn, how scanners decode it.
What is a symbology?
A symbology is one specific way of turning data into a printed barcode. It defines all of:
- The character set - what characters can be encoded
- The module patterns for each character - the actual bar-and-space sequences
- The start and stop characters (or guard patterns ) that bracket the data
- The check digit (if any)
- The minimum quiet zone , dimension constraints, and decode algorithm
EAN-13, Code 128, QR Code, Data Matrix, Aztec - these are symbologies. They are not data; they are specifications for how data is rendered as bars or modules. A single underlying number can be encoded as many different symbologies; conversely, a single symbology can carry many different kinds of data.
Symbology vs identifier
The distinction trips up newcomers more than anything else. Consider a tin of beans:
The GTIN-13 printed on the can: 5901234567893. It is what the can is - a particular SKU registered against a company prefix.
The EAN-13 barcode used to print it. It is how the GTIN-13 is rendered. The same GTIN-13 could equally appear in a GS1 DataBar, a QR Digital Link URL, or a GS1-128.
When you see "GTIN-13" written somewhere, that's an identifier; when you see "EAN-13", that's a symbology (one of several you could use to print that GTIN-13). Most data fields in this glossary are identifiers; most printed-barcode pages are symbologies.
The symbology family tree
1D linear - module-based
Every bar and space is an integer number of modules. The most reliable family for retail and logistics.
1D linear - width-based ("2 of 5" family)
Each character has exactly two bar widths - narrow and wide. Older but still common in industrial and DoD applications.
- Code 3943-char alphanumeric; ISO/IEC 16388
- LOGMARSCode 39 + mandatory mod-43 check; MIL-STD-1189B
- CodabarLibrary + blood bank; A/B/C/D start-stop
- Interleaved 2 of 5Numeric only, two digits per character pair; ISO/IEC 16390
- ITF-14Fixed 14-digit GTIN on outer cases
1D stacked
Multiple rows of 1D codes stacked vertically. Carries more data than a single row would.
- PDF417ID cards, boarding passes; ISO/IEC 15438
- MicroPDF417Compact PDF417 variant; ISO/IEC 24728
- CODABLOCK-FStacked Code 128 rows
2D matrix
A grid of modules with built-in error correction. Can be read upside-down, partially damaged, or off-angle.
- QR CodeConsumer-facing 2D; ISO/IEC 18004
- Data MatrixPharma + DPM workhorse; ISO/IEC 16022
- GS1 DataMatrixData Matrix with FNC1 + GS1 AIs
- Aztec CodeTransit ticketing; no quiet zone needed; ISO/IEC 24778
- MaxiCodeUPS shipping labels; hexagonal modules; ISO/IEC 16023
4-state / height-modulated
Special-purpose postal codes where each bar is the same width and information is carried by the bar height (one of four states).
- USPS Intelligent MailEvery US mail piece since 2013; USPS-B-3200
- PLANET CodeLegacy USPS tracking; superseded by IMb
Composite
A combination of two symbologies in one printed symbol.
- TLC39Code 39 primary + MicroPDF417 secondary; telecom equipment
Where symbologies come from
Most modern symbologies are defined by one of three standards bodies, with overlap:
- AIM Global - the original Automatic Identification Manufacturers trade association. Its Uniform Symbology Specifications (USS) defined Code 39, Code 128, Codabar, Code 93, and most of the 1D family in the 1980s and 90s. Many AIM specs were later adopted by ISO/IEC verbatim.
- ISO/IEC JTC 1/SC 31 - the international standards committee for automatic identification. Publishes the modern barcode specs (15420 for EAN/UPC, 15417 for Code 128, 18004 for QR, etc.). These are the citations you'll see throughout this glossary.
- GS1 - not a symbology body, but the assigning authority for retail and supply-chain identifiers (GTIN, GLN, SSCC). GS1's General Specifications say which symbology to use for which application context - it doesn't define the symbology itself, it picks one and constrains its parameters.
A few symbologies sit outside this triangle: USPS Intelligent Mail comes from the US Postal Service; TLC39 from the Telecommunications Industry Forum; LOGMARS from US DoD MIL-STD-1189B; MaxiCode originated from UPS.