English: Structure of the Johab encoding (the ISO 646 based version, as opposed to the EBCDIC based version). First byte is on the Y axis, second byte (when applicable) on the X axis.
Legend
Yellow: ISO 646 (KS X 1003 with ₩—or ASCII with \), no second byte
Green: Hangul syllables (11172 characters), modern jamo (67 characters) and empty block (arguably an alternative encoding of U+3000 or U+3164)
Dark green: Hangul blocks with missing initial or missing vowel (520 characters), not always implemented
Red: "special characters", i.e. non-Hanja, non-Hangul characters (such as punctuation), plus historic Hangul jamo