Vertical type metrics
The baseline is the imaginary line that all the letters and numbers sit on. The x-height is the height of the lowercase x (the x is the only lowercase letter that is normally flat both top and bottom). However, I saw it called a mean line in a diagram on a typography Web site the other day, although I have never actually heard anyone use that term. Ascenders are the portions of lowercase letters that rise above the x-height as in b, d, f, h, k, and l. A t doesn’t ascend far enough to be called an ascender, usually. Descenders are the portions that sink below the baseline as in g, j, p, q, and y. The cap height is the height of the uppercase letters.
The reason that x is specified is that curves have to extend over the lines to look the proper height. Yes, it is an optical illusion. The same is true of letters such as A or V that have points. If the point does not protrude past the guidelines, the letter looks obviously too short. Even people who know nothing about type will know that something is wrong. Type design has many of these understandings that have become rules.
If you look above, you will see that even the x does not fit exactly in the x-height for this font (Palatino). You can even see that for this font the ascenders of the d and the h are different. You will discover that this optical alignment is crucial to excellence in type. You need to even align the sides of the columns optically to make them seem straight, clean, and perfect.
You can see below a font that fits the way it is supposed to. It’s Futura. However, it is a little boring, don’t you think? This is the dilemma. If you fit the mould too well, you lose most of the visual interest. However, if you are too far outside the mould, you look unprofessional.
TERMS: Some of you may have noticed that we just used two old letterpress terms. Most of you didn’t. Those two terms are uppercase and lowercase. The original terms were majuscules for large letters and minuscules for handwriting using small letters. Majuscules came to be called capital letters. Minuscules remained a mouthful. Uppercase and lowercase come from common typesetting practice where two wooden cases of letters were used in a standard setup. The upper case contained all the capital letters. The lower case contained all the minuscules. In other words, the common phrase caps and lower case (or C&lc) is just one of those things we do in English.
Some glyph terminology
Before we get into specifics, we need to define a few descriptive terms to help you see some of the differences between the categories. The terms are a little esoteric, but I think you will find them helpful to categorize things in your own mind. They will also help when buying fonts to make good choices.
- Stems: the vertical strokes in letters like h, k, l, r and so on.
- Bowls: the rounded parts of letters like b, d, g, o, p, and even c and s, according to some.
- Crossbars: the horizontal strokes on A, H, e, and so on.
- Head and foot serifs: the serifs at the top and bottom of a stem as in h, l, k, and d.
- Adnate or bracketed serifs: serifs that flow smoothly (often gracefully) out of the stems.
- Abrupt serifs: cross strokes at the end of stems with no bracketing.
- Terminals: the endings of the curved portions of letters like a, c, r, C, G, and so on.
- Lachrymal: terminals that are tear-drop shaped.
- Stroke: the lines that make up the characters from the old assumption that letters are calligraphic and drawn with separate strokes of a pen or brush.
- Modulated stroke: a stroke that varies in width as it proceeds around the letter form.
- Axis: the angle the pen was held at to produce the modulated stroke of calligraphers.
- Humanist axis: the axis for normal right-handed calligraphic penmanship.
- Contrast: how much the stroke is modulated.
- Aperture: the openings of curves on letters like a, c, e, s, and so on.
- Slope: how far italic and oblique letters slant in degrees.
There are more, but this will be enough for our purposes. As you can see, type gets very technical. The differences will seem insignificant to you now, as you start. But they are really very important. Aperture, for example, tends to control the friendliness and readability. The axis changes from humanist to mechanical vertical strongly influence our reaction to the warmness or coolness of a font. But we’ll discuss these things as we go, giving you examples so you can see the differences.