Keep It Consistent, Except ...
Leading, like much in typography, is about rhythm, and as with a piece of music, you want your rhythm to be steady and unfaltering. The best way to achieve this is to set the leading values within paragraph styles. Should you need to change the leading values, you can edit the style definition rather than work on the text locally.
When it comes to fixing widows and orphans, don’t mess with the leading. You have other tricks up your sleeve—rewriting, tracking, adjusting word and letter spacing, discretionary hyphens, forced line breaks—to fix such problems. Tempting though it may be to tighten the leading a little here and there, your document will suffer if you do. Keep your body text leading consistent; otherwise, the rhythm of your type will wander like the beat of a distracted drummer.
USING OPTICAL LEADING
A: Because there are no descenders for line 3, the leading between lines 3 and 4 appears bigger.
B: The leading for the fourth line has reduced to compensate for there being no descenders on the line above.
Also, don’t be tempted to go for the quick ’n’ dirty solution of using vertical alignment, which increases the leading in a short column to make it bottom out (that is, end on the same baseline as other columns). While columns of uniform depth are preferable in continuous prose, InDesign can achieve this with the Balance Columns feature, which adjusts the height of all columns rather than just extend the shortest one.
There may be times when you need to relax consistency in favor of optical leading and tweak the leading of individual lines to make the leading appear more consistent. Such a situation may arise in display type if one line lacks descenders.
When Leading Gets Ignored
There are two scenarios when your leading value is overruled:
Baseline grid. If your text is aligned to a baseline grid, the grid increment trumps your leading value. For example, if you have a 12-point baseline grid and you increase the leading of text aligned to that grid to 13 points, the leading rounds up to the next grid increment of 24 points. See Chapter 16, “Pages, Margins, Columns, and Grids,” for more details.
LEADING AND BASELINE GRIDS
When using a baseline grid, the grid increment trumps the leading value, as in the right column. Increasing the leading causes the lines of the paragraph to snap to the next available grid increment.
A: Memphis Medium 10/12, aligned to grid
B: Memphis Medium 10/12.1, aligned to grid
Vertical justification. The Text Frame Options dialog box (Cmd/Ctrl+B) contains the Align pop-up menu, which you can use to force your text to vertically align within its text frame. Choose Align > Justify, and the leading value becomes irrelevant. The text fills the vertical space of the frame, regardless of how much space it has to add between the lines to do so—almost always a bad idea. To use vertical justification without overriding your leading values (a slightly better option), increase the Paragraph Spacing Limit so that InDesign can add space between the paragraphs instead of between the lines of text. See Chapter 7, “Alignment.”
Leading is one of the most important factors contributing to the readability of text. It ain’t rocket science, but there are a number of variables to consider. While there’s no single “right” leading value, there are plenty of inappropriate amounts. To sum it up: Avoid Auto Leading (except for inline graphics), think about the purpose—as well as the characteristics—of the type you’re working with, and exercise a strong degree of common sense. And always trust your eyes.