Can you tell your 1 from your l? Why letter legibility is key in type design

We take a look at graphic designer Thomas Bohm’s report, which explores the importance of typeface designers distinguishing between easily confused letters and symbols.

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Graphic and branding design teams often agonise over the perfect colour palette, imagery or tone of voice – so much so that the words and letters in a project can sometimes be overlooked. While choosing the logotype is always a considered decision, it’s easy to forget that even the simplest typefaces have characters that can be misconstrued, particularly for people with problems deciphering letters.

That’s why graphic designer Thomas Bohm, director of User Design, Illustration and Typesetting, has written a guide to help designers define letters and symbols that are often misrecognised when used in common, legible typefaces.

Looking at different audiences

Bohm’s report looks at misread characters from the viewpoint of children, those with dyslexia, those who are visually impaired, older people, and those who have no visual impairments and are aged 13-45 – a “general” population.

His inspiration for investigating the topic stemmed from the comparison of Erik Spiekermann’s Nokia typeface used on an old mobile phone, which had clearly defined the letters I (capital i), l (lowercase el) and 1, with more modern typefaces, which don’t define the letters as clearly.

“I always think – defining characters such as ‘I, l and 1’ would not affect a typeface drastically or negatively but would make it clearer,” says Bohm. “So why don’t typeface designers define these characters?”

Inclusivity in typeface design

He adds: “I have a passion for making graphic communication design highly usable. And by including aspects such as sight, age and disability into the paper, I thought it could make for an interesting and inclusive read.”

Bohm starts the paper by saying that different people misconstrue different letters and symbols, and confusion can occur in different situations – from reading a book to more “serious” situations such as misreading medicine information leaflets.

His report is composed of research and investigative work carried out on secondary sources. Here is a summary of Bohm’s findings:

Confusing letters and symbols for:

“General” people (aged 13-45, with no dyslexia or visual impairments)

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  • Lowercase l (el), uppercase I (i) and numbers 1 and 7 are easily confused.
  • Research has found that distinction can be made by use of serifs, bottom tails and top arms.
  • Confusion also arises between lowercase i and lowercase j, uppercase B and the number 8 and uppercase D and number 0 (zero). Quotation marks can also be misconstrued for inch and feet marks, and fraction marks with division signs.
  • Letter combinations can also cause confusion, such as “cl” being seen as “d”, and “rn” as “m”.
  • Condensing typefaces to superscript can cause problems with particular letters, such as number 5 and uppercase S.

Children (aged 4-12)

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  • Some letters are specifically adapted into “infant characters” for children, the simplified version of the letter ‘a’ being a key example.
  • These letters are becoming more popular in branding and advertising design, but can be confusing.
  • The infant “a” is problematic as it can be confused for lowercase o (ow) or number 0 (zero).

People with dyslexia

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  • Difficulties with letters that have similar character form design.
  • Those with dyslexia struggle to identify characters such as lowercase l (el), number 1, exclamation mark (!), lowercase o and uppercase O, p and q, b and d, among others.
  • Typeface features which help people with dyslexia read more clearly include longer ascenders and descenders on letters such as “h” and “p”, uniform stroke widths and writing at a 90° angle rather than a slant.
  • Christian Boer’s font Dyslexie is made specifically for people with dyslexia.

People with visual impairments

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  • Different eye conditions will affect people in different ways. The majority of those with visual impairments are aged 65+.
  • Letters with similar forms are difficult to distinguish between – such as uppercase U and uppercase V, number 5 and uppercase S, and number 8 and uppercase B.
  • Features that aid reading include using sans serif, enlarged spacing, bold letters, larger punctuation marks and un-italicised type.

Older people (aged 45+)

  • They will encounter similar difficulties to those with visual impairments.
  • Additional features to aid reading include consistent stroke width, pronounced ascenders and descenders and use of tails to distinguish characters.
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Bohm concludes his report by saying that neglecting to define letters and symbols can not only result in word confusion, but also “fatal incidents”. He advises that typeface designers use programs such as OpenType to amend and alternate particular letters in a defined typeface. “One of a designer’s social responsibilities is to make sure the design and communication they produce can be used well by the many different types of people who use it,” he says.


Read Bohm’s full report on “Letter and symbol misrecognition in highly legible typefaces for general, children, dyslexic, visually impaired and ageing readers”.

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