Type is defined by the space around it, whether between letters, words, or lines.
Monospaced versus Proportional
Fonts on typewriters were usually monospaced (also known as fixed pitch). Monospaced means that each character, whether it’s an i or an m, takes up the same amount of space. Monospaced digital fonts, such as Courier, work well when a mechanical typewriter look is desired or in cases where characters should line up vertically.
Today, most of the digital type used on computers is designed to be proportionally spaced. With proportional spacing, each letter is given just the amount of space it needs to look right and be most legible. Using a proportional font, you can fit much more text on a page than using a monospaced font while at the same time making the text easier to read.
As lines of text get long, it can be difficult for the reader to move from the end of one line to the beginning of the next. On the other hand, short line lengths break up the text and interrupt the reader. The ideal line length depends on the design of the typeface, type size, line spacing, and length of the copy. Generally, a line should have 55 to 60characters, or 9 to 10 words, for optimal readability.
Leading is the vertical distance between lines of type and is measured in points. During the days of metal type, printers inserted extra strips of lead between long lines of text to make them easier to read. This procedure gave rise to the term leading (pronounced ledding). Leading is measured from the baseline of one line of text to the baseline of the next line of text. Most word processing and page layout applications let you adjust the leading in your documents. Experiment with this feature to see how it affects legibility.
Word and Letter Spacing
You can also adjust word and letter spacing to improve legibility. Although typefaces are designed with the correct spacing between characters for general use, special situations can result in the type looking crowded or too loose. For example, words printed in all UPPERCASE tend to look too tight because the designer assumed that uppercase and lowercase letters would be mixed. If your application allows you to adjust letter spacing, you should add a small amount of letter space to words printed in all uppercase.￼
Some letter combinations, particularly in words set in capitals, result in awkward spacing unless they are kerned. Kerning is the adjustment of space between pairs of letters. Kerning is especially important at large point sizes. As the characters are enlarged, so is the space between them.
￼Word spacing, the space between words, should be constant in flush left, flush right, or centered text. However, for justified text, word spacing varies from line to line to keep margins even.
To aid readability, it’s important to keep word spacing as consistent as possible—even if it means hyphenating words. Tight word spacing lets you place more text on the page, but can make it difficult to distinguish words from each other. Loose word spacing fills up a page with a small amount of text, but the text becomes harder to read as the words begin to look disconnected.