Spacing and leading

Spacing inside a line comes from tracking and kerning; spacing between lines comes from leading.

In short Tracking adds the same space after every character of a run, in thousandths of an em. Kerning adjusts the space between particular pairs of characters: KerningMethod chooses how it is computed (InDesign writes $ID/Metrics, $ID/Optical or $ID/None), and KerningValue adds manual kerning. Leading is the distance from one baseline to the next, in points or Auto, which is the point size times the paragraph's AutoLeading percentage. BaselineShift moves glyphs up or down, and HorizontalScale, VerticalScale and Skew distort them.

Tracking

Tracking is in thousandths of an em, so its effect scales with the type size: at 12 pt, a Tracking of 100 adds 1.2 pt after each character, and a negative value tightens the run. It is a character attribute, set on a range or a style.

Kerning

Kerning is the space between two specific characters, such as the tighter fit of "To" or "AV". KerningMethod chooses where automatic kerning comes from, and InDesign writes its values in the reserved $ID/ namespace:

The census of real documents shows the prefixed spelling throughout: $ID/Metrics on paragraph styles in 271 documents and $ID/Optical in 8, and $ID/Optical on runs. No bare Metrics or Optical appears among the recorded values.

KerningValue is manual kerning: an amount in thousandths of an em added to the automatic kerning at that position, set on the range it applies to.

In Paged: kerning is applied by the shaper from the font's pairs. The $ID/-prefixed values are not recognised yet: every one of them, $ID/None included, falls back to metric kerning. The bare value None does turn kerning off, and optical kerning is not implemented (it is set like metric kerning). KerningValue is not read yet. These are known engine issues. Parsed, partly rendered

Leading

Leading is the distance from one line's baseline to the next. InDesign treats it as a character attribute: each line takes the largest leading among the runs on it. On a range or a style it is a typed <Properties> child:

• <Leading type="unit">14</Leading> — 14 pt;
• <Leading type="enumeration">Auto</Leading> — auto leading.

Auto leading is the point size times the paragraph's AutoLeading percentage, 120 by default. A line with mixed sizes gets the auto leading of its largest size. AutoLeading is a paragraph attribute, so different paragraphs can use different percentages.

In Paged: leading in points is applied, from either the typed child or an attribute. Auto leading uses 120 % of the size; a paragraph's own AutoLeading percentage is not read yet.

Supported · verified

Baseline shift, scaling and skew

Attribute · CharacterStyleRange	Values	Paged	paged.set
Tracking	number	read · written	characterTracking
BaselineShift	length (pt)	read · written	characterBaselineShift
HorizontalScale	number (percent)	read · written	characterHorizontalScale
VerticalScale	number (percent)	read · written	characterVerticalScale
Skew	number (degrees)	read · written	characterSkew
KerningMethod	Metrics | Optical | None	read · written	characterKerningMethod
KerningValue	integer	not read

BaselineShift moves the glyphs off the baseline by that many points, up for positive values, without changing the leading. HorizontalScale and VerticalScale stretch the glyphs as a percentage (100 is unchanged). Skew slants them by that many degrees, a false italic.

In Paged: baseline shift, both scales and skew are applied.

Supported · verified Supported · verified Supported · verified

Frequently asked questions

How does InDesign write KerningMethod values? With the $ID/ prefix: $ID/Metrics, $ID/Optical and $ID/None. A reader should accept that spelling; a writer should produce it.

What is the difference between metric and optical kerning? Metric kerning uses the kerning pairs the font designer built into the font. Optical kerning ignores them and computes the spacing from the shapes of neighbouring glyphs. None turns automatic kerning off.

What unit is Tracking in? Thousandths of an em, so it scales with the type size: 100 at 12 pt is 1.2 pt per character.

How is auto leading computed? The point size times the paragraph's AutoLeading percentage, 120 by default. On a line with mixed sizes, the largest size decides.