The vertical space between lines of type is called leading (rhymes with sledding). For Roman type, leading is measured from the baseline of one line of text to the baseline of the line above it. The baseline is the invisible line on which most letters sit. You can apply more than one leading amount within the same paragraph; however, the largest leading value in a line of type determines the leading value for that line.
When working with horizontal Asian type, you can specify how leading is measured, either from baseline to baseline or from the top of one line to the top of the next.
Kern and track
Kerning is the process of adding or subtracting space between specific pairs of characters. Tracking is the process of loosening or tightening the spacing between the characters in selected text or an entire block of text.
Values for kerning and tracking affect Japanese text but normally these options are used to adjust the aki between Roman characters.
You can automatically kern type using metrics kerning or optical kerning. Metrics kerning (also called auto kerning) uses kern pairs, which are included with most fonts. Kern pairs contain information about the spacing of specific pairs of letters. Some of these are: LA, P., To, Tr, Ta, Tu, Te, Ty, Wa, WA, We, Wo, Ya, and Yo. Metrics kerning is set as the default so that specific pairs are automatically kerned when you import or type text.
Some fonts include robust kern‑pair specifications. However, when a font includes only minimal built‑in kerning or none at all, or if you use two different typefaces or sizes in one or more words on a line, you may want to use the optical kerning option. Optical kerning adjusts the spacing between adjacent characters based on their shapes.
A. Original text B. Text with optical kerning C. Text with manual kerning between W and a D. Text with tracking E. Cumulative kerning and tracking
You can also use manual kerning, which is ideal for adjusting the space between two letters. Tracking and manual kerning are cumulative, so you can first adjust individual pairs of letters, and then tighten or loosen a block of text without affecting the relative kerning of the letter pairs.
When you click to place the insertion point between two letters, kerning values appear in the Character panel. Similarly, if you select a word or a range of text, the tracking values appear in the Character panel.
Tracking and kerning are both measured in 1/1000 em, a unit of measure that is relative to the current type size. In a 6‑point font, 1 em equals 6 points; in a 10‑point font, 1 em equals 10 points. Kerning and tracking are strictly proportional to the current type size.
Values for kerning and tracking affect Japanese text, but normally these options are used to adjust the aki between roman characters.
To use a font’s built‑in kerning information for selected characters, select Metrics for the Kerning option in the Character panel.
To automatically adjust the spacing between selected characters based on their shapes, select Optical for the Kerning option in the Character panel.
To adjust kerning manually, place an insertion point between two characters, and set the desired value for the Kerning option in the Character panel. (Note that if a range of text is selected, you can’t manually kern the text. Instead, use tracking.)
Press Alt+Left/Right Arrow (Windows) or Option+Left/Right Arrow (Mac OS) to decrease or increase the kerning between two characters.
Shift the baseline
Use Baseline Shift to move selected characters up or down relative to the baseline of the surrounding text. Shifting the baseline is especially useful when you’re hand-setting fractions or adjusting the position of a picture font.
Turn fractional character widths off or on
By default, the software uses fractional character widths between characters. This means that the spacing between characters varies, and will sometimes use only fractions of whole pixels.
In most situations, fractional character widths provide the best spacing for type appearance and readability. However, for type in small sizes (less than 20 points) displayed online, fractional character widths could cause type to run together or have too much extra space, making it difficult to read.
Turn off fractional widths when you want to fix type spacing in whole-pixel increments and prevent small type from running together. The fractional character width setting applies to all characters on a type layer—you cannot set the option for selected characters.