Readability and Legibility

Legibility and Readability.

Legibility is concerned with the very fine details of typeface design, and in an operational context this usually means the ability to recognise individual letters or words. Readability however concerns the optimum arrangement and layout of whole bodies of text.

An illegible type, set it how you will, cannot be made readable. But the most legible of types can be made unreadable if it is set to too wide a measure, or in too large or too small a size for a particular purpose.( Dowding 1957, p.5; in Lund, 1999 )

Typographic clarity is separated into two sections, legibility and readability. What’s the difference? Legibility is a function of typeface design. It’s an informal measure of how easy it is to distinguish one letter from another in a particular typeface. Readability, on the other hand, is dependent upon how the typeface is used. Readability is about typography. It is a gauge of how easily words, phrases and blocks of copy can be read. Legibility is a trait, not always a goal.

Three Aspects of Legibility

A long-standing typographic maxim is that the most legible typefaces are “transparent” to the reader–that is, they don’t call undue attention to themselves. Additionally, the most legible typefaces contain big features and have restrained design characteristics. While this may seem like a typographic oxymoron, it’s not. “Big features” refers to things such as large, open counters, ample lowercase x-heights, and character shapes that are obvious and easy to recognise. The most legible typefaces are also restrained. They are not excessively light or bold, weight changes within character strokes are subtle, and serifs, if the face has them, do not call attention to themselves. Counters, the white space within letters such as ‘o,’ ‘e,’ ‘c,’ etc., help to define a character. Typographers believe that large counters are an aid to character recognition. A byproduct of open counters is usually a large lowercase x-height. As long as the x-height is not excessively large, this can also improve legibility in a typeface. Because over 95% of the letters we read are lowercase, larger letter proportions usually result in a more legible typeface.

Legibility in Typography

Legibility in typography generally requires large, open counters and ample lowercase x-heights. Weight changes are subtle and serifs are not dominant. Not all typefaces are, or should be created with legibility as a primary design function. Many faces are drawn for the purpose of creating a typographic statement, or for providing a particular spirit or feeling to graphic communication. Some typefaces are just designed to stand out from the crowd. To the degree that a typeface has personality, spirit, or distinction, however, it almost always suffers proportionally on the legibility scale.

While virtually any serif typeface can benefit from large open counters, “Clarendons” like Nimrod or Scherzo and contemporary interpretations of “Old Style" designs, such as Monotype Bembo and ITC Weidemann, tend to come by this trait most naturally. Individual letter shapes can also affect typeface legibility. For example: the two-story ‘a’ such as the one found in Stellar or Exlibris is much more legible than the single-story ‘a’ found in Futura or Erbar. The lowercase ‘g’ based on Roman letter shapes is more legible then the simple ‘g’ found in Helvetica or Glypha. In Old Style typefaces such as Monotype Plantin, Galena and ITC Berkeley Oldstyle, individual characters have more personality than those in traditional “legibility” faces with virtually no loss in character legibility.

While the argument continues to rage about whether sans serifs are easier to read than serif fonts in text copy, sans serif typefaces, because their letter shapes are simpler, have been proven to be slightly more legible than their serifed cousins.

Another potential drawback of serif typefaces is that the legibility of individual letters suffers when serifs have exaggerated shapes. Long serifs, those that are exceptionally heavy and those with unusual shapes all detract from legibility. Ideal serifs are somewhat short and slightly bracketed. They are also heavy enough to be obvious yet not conspicuous. Typefaces such as Monotype Sabon and ITC Stone have great serifs. Lighter typefaces are usually more legible than heavier weights of type. They allow for full, open counters and unmodified character shapes. Studies have shown that the best character stroke thickness for text typefaces is about 18% of the x-height. Typefaces with weights similar to that of Albertina Regular, ITC Officina Sans Book and Cartier Book Roman fall into this general category.

The metaphor of “transparent type” was coined by Beatrice Warde, Monotype Imaging's famous marketing manager of the 1930s and 40s. She once wrote in an article that good type is like “a crystal goblet” which allows content to be more important than the container. Warde contended that the best types do not get in the way of the communication process: these faces are virtually invisible and allow words to make the statement not the type. While this is sage advice, if this principle were followed rigidly, graphic communication would be about as exciting as a head cold. This does not mean that legible typefaces can’t be distinctive in design, or that we should be using Ionic No. 5 for all typography. Some distinctive typefaces, such as Truesdell, Agfa Rotis, or Alinea, also make fine legibility fonts. The metaphor is, after all, a crystal goblet–not an empty jam jar.

Situational Typography

Specific situations or contexts can also affect typeface legibility. For example, if copy has a lot of numerals, a sans serif face may be the best choice. The reason? Sans serif numerals are simpler and have more recognisable character shapes than their roman counterparts. There are times when you have a lot to say and not much room in which to say it. In instances like these, faces with condensed proportions are the best choice. Condensed typefaces of light to medium weight also work well in cramped typographic quarters because their counters are not prone to filling in. Sans serif faces are almost always the safest choice because their individual character shapes tend to be more legible. A serif typeface such as ITC Garamond Condensed or Galena Condensed can be effective as small as 8 point or 9 point, but when smaller sizes are required, a sans serif like Generica Condensed or Abadi Condensed are better options.

Even though virtually anyone can set type today, there are still many skills that separate the typographer and graphic designer from the desktop publisher. Picking the absolute best, and sometimes the most legible typeface is one of those skills.

Typographical features.

There are many elements in the design of a typeface which can contribute to its legibility.

Serif / Sans Serif

“Serifs” are the small finishing strokes on the end of a character. “Sans serif” fonts do not have these small finishing strokes.

Point size

Point size is perhaps the element most used to describe the legibility of a type face, but it can also be the most deceptive. Point size is a legacy from the letterpress system, where each letter is held on a small metal block. The point size actually refers to the size of this metal block, and not the actual size of the letter. The letter does not have to take up the full area of the block face, so two fonts with the same nominal point size can quite easily have different actual sizes. ( Bix, 2002 )

X-height

X-height refers to the height of the lower case “x” in a typeface. It is often a better indicator of the apparent size of a typeface than point size ( Poulton, 1972 ; Bix, 2002 )

Counters

Counters are the “negative spaces” inside a character. They are also good indicators of the actual size of the type.

Ascenders and descenders

Ascenders and are the vertical strokes which rise above the body of a character or x-height. Descenders are strokes which fall below the baseline of the x-height.