Designing the Whitespace

A glyph's drawing and its surrounding space work together. The outlines determine the visible form; the spacing determines how that form meets its neighbors. Even an unfinished glyph already has an advance width and a position within it. Spacing makes those provisional relationships deliberate.

Form and Counterform

Look at a word before inspecting its individual letters. The alternation of strokes and spaces creates a rhythm. Across a paragraph, that rhythm contributes to typographic color: the overall tone produced by balancing inked and uninked areas within and between glyphs. Its consistency is a target of good spacing, rather than a literal ink color.

The white inside and around a letter is part of its design. A counter is the whitespace enclosed or partly enclosed by its strokes. The interior of o is an enclosed counter; the opening inside n is partly enclosed. The exterior spaces next to these forms need to relate to those internal spaces without necessarily matching them numerically.

A shape can look balanced by itself yet interrupt the rhythm of a word. A wide counter with very tight external spacing can make adjacent letters crowd together. Generous external spacing around a narrow interior can make the letter appear detached. Judge both the positive form and the counterform—the shape of the surrounding and internal white.

The type designer establishes useful default spacing in the font. A typographer can later apply tracking, a uniform spacing adjustment to a run of text, to suit a size, layout, or purpose. Tracking changes the run's overall fit; it does not repair every uneven relationship built into individual glyphs.

Establish the defaults without simulated tracking or applied kerning obscuring them. Then test the design at realistic sizes. Enlarging the canvas is useful for precise work, but the rhythm of text is also a visual judgment made at the sizes where the font will be read.

Sidebearings and Advance Width

In metal type, the letter stood on a body with shoulders around its printing surface. In digital type, the drawing occupies a coordinate space and has a horizontal advance width. The glyph's position within that interval leaves—or overhangs—the clearances called sidebearings.

For ordinary upright, bounding-box measurement:

  • The left sidebearing (LSB) is the signed distance from the glyph's origin at x = 0 on the baseline to the drawing's leftmost extent; recall The Em and the Coordinate System.
  • The right sidebearing (RSB) is the signed distance from the drawing's rightmost extent to the advance boundary.
  • The advance width is the distance from this glyph's origin to the next glyph's origin before pair or other layout adjustments.

The glyph bounding box is the smallest rectangle enclosing this glyph's relevant drawing. Its width excludes the sidebearings. It is distinct from the font-wide bounding box, which records the combined extent of the font's drawings.

The relationship is:

advance width = LSB + bounding-box width + RSB

For a drawing extending from x = 40 to x = 540 in a 600-unit advance, the drawing width is 500, the LSB is 40, and the RSB is 60. Moving the drawing 10 units right while keeping the advance at 600 changes the bearings to 50 and 50. Increasing the advance by 10 without moving the drawing instead changes only the RSB to 70.

A sidebearing can be negative. If the left edge lies at x = −20, the glyph overhangs its origin by 20 units. If the right edge lies beyond the advance boundary, the RSB is negative. FontLab's ordinary width editing prevents an advance width below zero; zero-width glyphs remain possible.

A space glyph can have an advance width with no visible outline. Its advance still contributes whitespace to text. Conversely, a visible mark can have zero advance and depend on positioning rather than ordinary letter spacing.

These measurements describe the available geometry; equal numerical sidebearings do not guarantee equal perceived space. A round edge recedes from its bounding box over much of its height, while a straight stem occupies more of that edge. This is one reason similarly sized round and straight letters can need different bearing values.

Italic metric views and the Metrics Line provide other ways to inspect clearance. The ordinary bounding-box relationship remains the starting model for understanding the stored fit.

Spacing and pair adjustments

Establish sidebearings that work across many neighbors, then use kerning for pair-specific exceptions. Avoid using pair adjustments to compensate repeatedly for a poor default bearing. Better defaults can reduce those compensating pairs, though the size of a kerning table alone does not prove weak spacing: character coverage, scripts, and the design also affect how many pairs are needed.

Spacing completes the glyph as a participant in text. Its success is the consistent rhythm of the resulting strings, not a particular set of sidebearing numbers.