Typographic approximation

For a printed medium (such as paper), a typographic approximation is a replacement (approximation) of some element of the writing system (usually, a glyph) with some else glyph(s), such as a nearly homographic character, digraph or character string. An approximation is different from a typographical error in that an approximation tries to preserve visual appearance of a glyph. There are approximation for non-printed visual presentation such as displays. The concept of approximation also applies to the World Wide Web and other forms of textual information available via digital media, though usually at the level of characters, not glyphs.

Historically, the main cause of typographic approximation was a low quantity of glyphs (such as letterforms and symbols), available for printing. In the age of World Wide Web and digital typesetting, especially after the advent of Unicode and enormous amount of digital fonts, typographic approximations are usually caused either by low ability of humans to distinguish and find needed symbols or by inadequate replacement patterns in word processors, rather than by shortage in available characters.

On typewriter, several characters were merged due to limited size of glyph repertoire. Several modern computing characters appeared by merger of different symbols, such as the "typewriter" apostrophe,', which can denote an apostrophe proper,’, a single quote, and the prime symbol.

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