Jan 14 2009

Inconspicuous vertical metrics

by Alec Julien

Five?

There are generally taken to be five vertical measures of note in type design (from bottom to top): descender, baseline, midline*, caps-height, and ascender.

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But if you delve into the minutiae of font design, you soon discover that there are a slew of important vertical metrics that aren’t much talked about. In this article, I will take a look at several of these metrics, and how they are used in font design.

t-height

Take a look at the basic alphabet from the venerable Minion, with the top three measures highlighted across each glyph:

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You’ll note that the lowercase ‘t’ sticks out like a proverbial sore thumb. The crossbar aligns with the font’s x-height, but the top of the glyph is on a vertical plane all its own. In my research, I find no accepted terminology to measure the top of the ‘t’, and so I propose we give a name to this vertical metric (simply enough): t-height.

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The tradition for serif types is, like with Minion, for the crossbar of the ‘t’ to be at the font’s midline line, and for the top stem of the ‘t’ to come up somewhere midway between the midline and the caps-height.

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Typically, sans serif faces adhere to the same rule, as do slab serifs. However, gothic and geometric sans faces often break with tradition and elevate the ‘t’ to the ascender. Handwriting fonts often do the same.

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Overshoot

Looking at the string ‘xoXO’, you might think that there are only three of the standard five vertical metrics in play: baseline, midline, and caps-height.

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But if you view these glyphs at a larger size, you can see that the bottoms and the tops of the ‘o’ and ‘O’ overhang the baseline and their respective constraining heights. This is standard practice in type design; the reason being that if the ‘o’ and ‘O’ came exactly to the baseline and x-height/caps-height, it would appear to the naked eye as if they were smaller than other surrounding glyphs. This goes for any glyph rounded on the top or bottom. Here are some typical lowercase overshoots, top and then bottom:

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And typical uppercase overshoots:

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In principle, the overshoots should not be apparent to the eye at normal text sizes. The whole idea of overshoots is that they make their glyphs appear to be the same height as flat-topped and flat-bottomed glyphs.

e-bar height

Typically, the bar of the ‘e’ rests somewhere between halfway and two-thirds up from the baseline to the midline. (It’s extremely rare to find a typeface where the bar of the ‘e’ is below the halfway point between the baseline and the x-height.) Let’s call the height of the center of the bar of the ‘e’ the e-bar height. Here are Minion, Helvetica, Times New Roman, and Museo, and how their e-bar heights compare to the A-bar height and the x-junction height:

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A-bar height

The A-bar height, taken as the measure from the baseline to the center of the bar of the ‘A’, typically ranges from around 30-40% of the distance from the baseline to the caps-height.

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Incidentally, as you can see from the above image, the H-bar height is generally higher than the A-bar height. This makes sense architecturally, if you think of the crossbars of these glyphs as providing a sort of balance. The ‘A’ crossbar, if it were up at the height of the ‘H’ crossbar, would make the ‘A’ rather top-heavy.

R-Junction, P-Junction, B-Junction, and K-Junction heights

When I first started designing fonts, I thought, naively, that the junction points in the middle of the vertical bars of the ‘R’, ‘P’, ‘B’, and ‘K’ were all at the same height. Wouldn’t it be easy if you could just design a ‘P’, and then just stick a leg on it for an ‘R’, and another hoop on it for a ‘B’? I soon learned better. Here, once again, is Minion to show us the subtle variations in vertical metrics that make a font interesting:

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Upon closer inspection, we can really see the different heights of these junctions. Here’s a close-up of the ‘R’ next to the ‘P’. Note that the P-junction height is slightly lower than the R-junction height.

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The B-junction height is much higher than the R-junction

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E-Junction and F-Junction heights

You might also suspect that the middle bars of the ‘E’ and ‘F’ would be at the same height, but this is not always the case.

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In Minion, the E-junction height is slightly higher than the F-junction height. You can see, also, that there is a wide variance of heights across the middles of some glyphs:

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Look how strange Minion would look if all of these middle heights were the same:

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And then some

We’ve really just scratched the surface. Well, I suppose we’ve dug in a little more deeply than the surface, but there are still a great many more interesting vertical metrics we could explore. G-bar height, briefly alluded to in the images above; foot serif height, and head serif height; two-storey a-junction height, or where the upper stroke of the bowl intersects with the vertical stem; two-storey g-bowl height, or how high the upper bowl of the ‘g’ starts above the baseline.

If your interest is piqued, I highly recommend Karen Cheng’s Designing Type, which is filled with wonderful analyses of minutiae like these.

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* midline should not be confused with x-height; strictly speaking, the x-height is the distance between baseline and midline.


Tags:    typography terms

  1. sjaq

    Great post, thanks! Now I have some more typo terms I can throw at my typography teacher at school ;).

    Jan 14, 2009

  2. Lasha

    Very good read! It’s a nice reminder of all the things I studied when I was taking Typography classes. This makes me wanna get into type design of my own, haha.

    Jan 14, 2009

  3. inspirationbit

    a person can get dizzy looking at typefaces from all those typographic heights ;) Great article! Thank you, Alec. At least, while ‘falling’ I’ve learned a lot about the passing heights ;)

    John, what happened to those distinctly iLT curly braces around the comments? :) I see much more “Lucida Grande” has been injected into the style. I like it, the site appears much cleaner now. But I’m not crazy about the comment/date styling.

    Jan 14, 2009

  4. Luke

    Great read as always, I wonder how much differences in these values would affect how a font is percieved. perhaps by lining up the R, K, F etc functions perfectly, you’d create an entirely differently effect. I do wonder…

    Jan 14, 2009

  5. Travis Neilson

    If the x-height refers to the space between the base and mid-lines, does the Cap-height have a similar reference to space? If so what is the propper term for the line which the 1st illustration refers to as a Cap-height?

    Wow, fantastic article! I never considered all of these factors. Thank you so much for sharing!

    Jan 14, 2009

  6. David Airey

    Intriguing, Alec. I appreciate these insights, and thanks for the book recommendation. I’ll definitely take a look.

    Johno,

    I clicked-through from my feed reader, and was greeted with a ‘StumbleUpon’ welcome message at the top of your post. Might want to look into that.

    Bye for now.

    Jan 14, 2009

  7. Rob Keller

    Travis,
    x-height and cap-height are the universally used terms, no one actually says midline.

    Jan 14, 2009

  8. Davide

    Very insightful Post. Thanks :-)

    Jan 14, 2009

  9. Rob Keller

    also,

    It is nice to see these details highlighted in this way. Most people do not realize the subtle differences to create optically even and ‘normal’ looking designs.

    However, I have never really thought of any of these as vertical metrics – with the exception of overshoot. Overshoot should certainly be in the same category as the “general 5 measurements” you mentioned. Do not forget though, there are 4 or overshoot lines: two each for upper and lowercase letters and maybe another for the descenders depending on the design. But overshoot is generally not mentioned because it’s value is numerically so close to the other lines, it is difficult to show.

    These other ‘measurements’ are very important for designers to consider, but fundamentally they are a different category. Those general 5 measurements are all guidelines that affect many or most letters – they travel through the whole design. These others measurements you mention are only used on a per glyph basis. It does not make sense to create the titles t-bar height or E-junction height etc.* They are optical and proportional relationships and are not really in the same category as the general vertical metrics measurement lines.

    *these terms are useful for discussing and critiquing typefaces though.

    Jan 14, 2009

  10. Julian Schrader

    Great post! Thanks a lot for this lesson—I’m looking forward for more :-)

    Jan 14, 2009

  11. Kári Emil Helgason

    Wow, and here I’ve actually been thinking that P, R, B had the same juncture hight as well as E and F. It looked like it made sense.

    Jan 14, 2009

  12. Silas

    Rob’s post +1. Well said. While all the nomenclature may not be necessary, the awareness of all these nuances is especially invaluable to fresh eyes. Cheers.

    Jan 14, 2009

  13. amon

    what an inspiring piece - thankyou

    Jan 14, 2009

  14. Dan Reynolds

    Rob Keller is right on. He speaks the truth!

    While I certainly applaud this article, I should add that the title is misleading. In type design, the term “Vertical Metrics” refers to something else.

    This article seems to me to be more about “Vertical Alignments.” In fonts, “Vertical Metrics” refer more to cetain values that will determine line spacing in applications.

    Jan 14, 2009

  15. Adam

    This is great! Thanks a lot.

    I’m sure that, like others, I’ll find an appropriate time to point some of this information out in the company of non-designers. And I’m also sure they’ll tut and give each other the “who invited the typographer” look!

    Keep the excellence coming!

    Jan 14, 2009

  16. gersk

    Many thanks for this article.
    I like details in typography (as well as in life).

    grsk

    Jan 14, 2009

  17. Alec

    Thanks, all!

    Rob, et al: I agree that these measures (would it have been better if I had called the article “Inconspicuous Vertical Measures”?) could be in a different ontological category from the standard five vertical metrics. If they weren’t, I suppose they would already have names and would be discussed more often. However, that said, they are measures, and a synonym for ‘measure’ is ‘metric’, so I don’t feel too bad in dubbing them as such. And even if each of these metrics only applies to one glyph, it still affects a typeface’s design and can be fruitfully compared against the same metric in other faces. Rob, you say “It does not make sense to create the titles” of these metrics. But how do you propose that we then talk about it? “The height of the t”? Is that really any better than saying “t-height”?

    In any event, the piece was not meant to be the beginnings of a nomenclature revolution, but just an analysis of vertical measures that don’t generally get much attention.

    Thanks for the comments, all. Keep ‘em coming!

    Jan 14, 2009

  18. Leandro

    I liked the post and also the comments. It’s nice to have a space of discussion like this one to learn some fundaments about typefaces.

    Jan 14, 2009

  19. Will Miller

    Great read. I teach a type 1 class and we’re just now starting to hit on these topics. Reinforces the idea that type design is a lot of balance and a lot of adjustment to make something look right.

    Jan 14, 2009

  20. Simon Pascal Klein

    Thank you for this in-depth analysis of my favourite typeface. I can also recommend Karen Cheng’s Designing Type (German: Anatomie der Buchstaben).

    Jan 14, 2009

  21. Troy H.

    Once we get done painting the exterior of the house, I know where I’m coming for address numbers (selection and placement) advice.

    Jan 14, 2009

  22. Jeff

    Thank you for your hard work. Really. I’ve learned a lot from your site.

    Jan 14, 2009

  23. Rock Kauser

    Great article. I learned a lot about type metrics. Thanks!

    Jan 14, 2009

  24. pienose

    great post! now I have more things to look at when I get bored in english lessons! and more terms to confuse my mates with =P

    Jan 14, 2009

  25. LaurenMarie - Creative Curio

    Yay! A learning article :) Alec, you are an awesome teacher. There is so much that goes into designing a typeface. It’s amazing. Now I’ll get even more eye-rolling from my husband and designer friends. Perfect ;)

    Jan 14, 2009

  26. Craig

    Aren’t t and J [in cases where they curve at the baseline] also typical overshoots at the bottom?

    Jan 14, 2009

  27. Jelmar

    When I learned to write, we always learned the t is supposed to be shorter than the ascenders. So this is a clear remnant of handwriting. Therefore any t’s that extend to the ascender height look silly to me.

    The crossbar of the F is usually placed slightly lower to optically compensate for the large open space below it.

    In FontLab, the only lines that fall under Vertical Metrics (i.e. appear/disappear when you show/hide them) are the Descender, Baseline, x-height, cap-height and Ascender lines.

    FontLab (and such) has even more lines! ;)
    They’re called ‘Alignment zones’, which are used for (auto)hinting.
    They can be set around all the Vertical Metrics I mentioned above.

    Jan 14, 2009

  28. Pedro Alberto

    Awesome article.
    I’m a beginner type-student (15 years old), so this is really handy.

    Thank you for this awesome blog.

    Jan 14, 2009

  29. Alec

    @Craig: Yup. ‘t’ and ‘J’ often overshoot the baseline.

    Jan 14, 2009

  30. Rob Keller

    Alec,

    I suppose I would have framed the article more like “inconspicuous vertical relationships” or something more of that nature.

    The nomenclature of many of these elements is not new, and as I mentioned earlier, they are useful in discussing type. But when describing a glyph it really doesn’t make much difference saying the “the height of the t” or “the t-height.”

    Dan pointed out rightfully that the metrics are primarily for vertical spacing of the fonts in applications, and they are also for things such as hinting. Overshoots would be in the “metrics” category as well, but these other measures are something else entirely.

    Again, good to point out the finer points of type design that don’t get enough attention. These are the details that can really make or break a design – slight adjustments of only a few units one way or another can make dramatic changes (in text typefaces at least).

    Cheers,
    Rob

    Jan 14, 2009

  31. Sebastian Nagel

    small caps height!

    Jan 14, 2009

  32. Flavio Hebaru

    very nice post!

    Jan 14, 2009

  33. Robert

    Great Article Alec. I never knew about e-bar and A-bar. Thanks for the information, and keep it comin’.

    Jan 14, 2009

  34. Mr. Smith

    Although I already knew a lot of this, there’s things you mentioned I’ve never really thought about. This was a good read, and I’m going to have to check out that book. Thanks!

    Jan 14, 2009

  35. Joshua N Taylor

    So I’ve always been curious if there is any sort of “rule” for overshoots, like how mush larger to make them. I know a steady rule is impossible, but a jumping off point would be nice.

    Jan 14, 2009

  36. Jos Buivenga (exljbris)

    Great post Alec!

    Joshua: There isn’t one rule. The overshoots of a display font need to be smaller as the ones for a text font. The overshoots also depend on the shape of the bowls. The flatter they are, the less overshoot is needed. Only trust your eyes ;-)

    Jan 14, 2009

  37. Alec

    @Sebastian: good one! Small caps generally are right around a font’s x-height. See this article for more than you ever wanted to know about Minion’s small caps.

    Jan 14, 2009

  38. Ole Schaefer

    … do not forget the figure set hights, old style figures, lining figures, tab figures, small caps figures, and small caps hights from text to display faces … however i am still working on an old typeface that also has different hights in the characters «t» and «f» and «o» or «e» … but it is good to see that people are intrested in «hight definitions».

    Jan 15, 2009

  39. reggyR

    A lot to take in but a great article. Thanks Alec and Johno!

    Jan 15, 2009

  40. jac

    wow! Great post! I do notice these little differences, but for you to blog about it and compare these fonts is true passion :)

    Jan 15, 2009

  41. syahrulfikri

    amazing. this is really great post!!!

    Jan 15, 2009

  42. Travis Neilson

    @Rob Keller I am aware that they are the common terms, but I was intrigued by the concept of the term x-height measuring space and i was wondering how far that thought could be followed.

    I remember when I learned that the aperture of a camera was not the little bit that opened up to let the light in, but actually the space that was created by that little bit when it opened. Similar revelation here. It struck me.

    So, does any one know; “strictly speaking,” if the x-height refers to the space between the base and mid-lines, does the Cap-height have a similar reference to space? If so what is the propper term for the line which the 1st illustration refers to as a Cap-height?

    Jan 15, 2009

  43. Rob Keller

    I am interested in knowing where the term ‘midline’ originated. I am suspicious of it’s invention and more importantly its use here…

    I believe you are correct Travis about it’s technical nature, although again I will reiterate that I don’t consider it to be the correct term for ‘everyday use.’ X-height is the standard definition for measuring the space between the baseline and the (relative) height of the lowercase characters. In my library, I only have two references to midline in my collections. The first is in Typo Magazine from July 2005 from an article by Krisztina Somogyi (and I believe it to be the improper use in this case). The second is from the Panose system specs. Their definition is “The Midline digit describes the placement of the midline and the treatment of diagonal stem apexes.” Honestly, I don’t fully understand that

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