Editing Aztec Code (section)

== Structure ==
The symbol is built on a square grid with a bull's-eye pattern at its centre for locating the code. Data is [[code|encode]]d in concentric square rings around the bull's-eye pattern. The central bull's-eye is 9×9 or 13×13 [[pixel]]s, and one row of pixels around that encodes basic coding parameters, producing a "core" of 11×11 or 15×15 squares. Data is added in "layers", each one containing two rings of pixels, giving total sizes of 15×15, 19×19, 23×23, etc.

The corners of the core include orientation marks, allowing the code to be read if rotated or reflected. Decoding begins at the corner with three black pixels, and proceeds clockwise to the corners with two, one, and zero black pixels.<!--But the message data is stored in reverse order.--> The variable pixels in the central core encode the size, so it is not necessary to mark the boundary of the code with a blank "quiet zone", although some barcode readers require one.

<gallery widths="280" heights="220" perrow="3">
File:Aztec Code with desc.png|The core of the compact Aztec code (red ascending diagonal hatching), showing the central bull's-eye, the four orientation marks (blue diagonal cross-hatching), and space for 28 bits (7 bits per side) of coding information (green horizontal hatching). The first ring of data begins outside that (grey descending diagonal hatching).
File:Aztec code full core.png|The core of the full Aztec code. 40 bits are available between the orientation marks for encoding parameters.<!--The full aztec code includes some fixed elements that use 4 pixels of the 44 between the orientation marks-->
File:Aztec Encoding.svg|Compact Aztec symbol encoding the message, 'Wikipedia, the free encyclopedia'. Message data is placed in a spiral pattern around the core. The mode message begins "01011100", indicating 01<sub>2</sub>+1 = 2 layers, and 011100<sub>2</sub>+1 = 29 data codewords (of 6 bits each). The message data is encoded using a (63,52) Reed-Solomon code (shortened to (40,29) and corresponding to 29 data words and 11 error correction words of 6 bits each) over GF(64). Error correction words are represented as E1 through E11. The mode message is protected by a (15,10) Reed-Solomon code (shortened to (7,2) and corresponding to 2 data words and 5 error correction words of 4 bits each) over GF(16).
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The compact Aztec code core may be surrounded by 1 to 4 layers, producing symbols from 15×15 (room for 13 digits or 12 letters) through 27×27. There is additionally a special 11×11 "rune" that encodes one byte of information. The full core supports up to 32 layers, 151×151 pixels, which can encode 3832 digits, 3067 letters, or 1914 bytes of data.

Whatever part of the symbol is not used for the basic data is used for [[Reed–Solomon error correction]], and the split is completely configurable, between limits of 1 data word, and 3 check words. The recommended number of check words is 23% of symbol capacity plus 3 codewords.<ref>{{cite web |url=http://www.adams1.com/stack.html |title=2-Dimensional Bar Code Page |first=Russ |last=Adams |access-date=2022-07-14 |url-status=dead |archive-url=https://web.archive.org/web/20100430184215/http://www.adams1.com/stack.html |archive-date=2010-04-30
}}</ref>

Aztec Code is supposed to produce readable codes with various printer technologies. It is also well suited for displays of cell phones and other mobile devices.