[Tex/LaTex] What exactly is leading

font-metricsline-spacingtypography

In typography, leading ( /ˈlɛdɪŋ/)
refers to the distance between the
baselines of successive lines of type.

By this definition, isn't it the same thing as line height?

But in the following examples in the same wikipedia page, it seems leading is extra space between lines, not line height. Otherwise, "no leading" should mean "no line height" which is obviously wrong. And 50%/100% leading seems to mean adding an extra inter-line spacing of 50%/100% natural line height.

Wikipedia is not the only source that holds contradictory content. Another website in the first search result page of "font leading" also gives contradictory graphical demonstrations.

And if you are an iOS developer, you may know that UIFont has a property called leading which returns line height. The fact that the property is now deprecated and replaced by a new property call lineHeight further shows how confusing this leading thing is.

I'm inclined to think leading as extra space added between lines. And here are two references that support this understanding:

A glossary of typographic terms

leading (pronounced: ledding)
The amount of space added between lines of text to make the document legible. The term originally referred to the thin lead spacers that printers used to physically increase space between lines of metal type. Most applications automatically apply standard leading based on the point size of the font. Closer leading fits more text on the page, but decreases legibility. Looser leading spreads text out to fill a page and makes the document easier to read. Leading can also be negative, in which case the lines of text are so close that they overlap or touch.
CTParagraphStyle Reference

kCTParagraphStyleSpecifierLineSpacing
The space in points added between lines within the paragraph (commonly known as leading). This value is always nonnegative. Type: CGFloat. Default: 0.0. Application: CTFramesetter.

Maybe leading is really misleading. I hope someone can tell me definitely what exactly leading is. But maybe leading is just a typographic term that can never receive a consensus, thus should be avoided as much as possible, and even be deprecated in preference for more clear and compatible concepts such as ascent, descent, line gap, and line height(line height = ascent + descent + line gap).

Best Answer

The easiest way to understand the meaning of leading is to get a piece of paper and draw two lines. On these two lines, write some text. the distance between these two lines is the leading.

enter image description here

When typesetting the only "constant" parameter for laying out text is the baseline. Descenders, diagritics and subscripts can extend below this line. That is why normally everything relates to the baseline and not the bounding box of the letters.

For a good article and leading definition "woos" see http://www.creativepro.com/article/just-say-no-automatic-leading and of course Knuth did not help much in calling it "baselineskip".

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I had this discussion once with a friend who had a printers education (Sorry, don't know the right english term). I don't remember the details, but basically she said that the setspace package doesn't calculate the line spacing correctly by it's universally defined formula. According to her, \linespread{2} sets the spaces correctly. However, I myself prefer setspace while working with a 1.5 line space, because I think it looks better. Maybe that was also the authors' intention.

(I would be happy if a more sophisticated answer comes along .)

[Tex/LaTex] Why exactly is \linespread{1.05} appropriate for Palatino

Some preliminary remarks. I think we can all agree that there can be no universally agreed-upon optimal amount of "typographic color" or "overall grayness" of a page of text. What some might consider to be "good color" may strike others as unpleasantly light, or too dark. Nevertheless, for the sake of the argument, let's assume that (i) there is an optimal amount of color and (ii) the settings for 10pt Computer Modern set "single-spaced" achieve this optimal amount. (By the way, this does not imply that the optimal distance between consecutive lines is 10pt for text set in CM. The topic of what exactly constitutes "single-spacing" is a matter for a different discussion.)

The question then becomes: how does one achieve this amount of color when switching to a different (text) font, such as Palatino? Palatino and CM obviously differ in many respects. Not only are their x-heights different, but so are their cap-heights and ascender heights as well as the average stroke width (to name just a couple of additional factors). The upshot is that if text that consists of a group of paragraphs is set both in Palatino and in CM with the same nominal point size (say, 10pt) and the same interline distance (say, 12pt), the paragraphs and pages set in Palatino will look noticeably darker. I think most will agree that the Palatino paragraphs will be "too dark" -- again, assuming that the text set in CM have "correct color".

Who exactly came up with \linespread{1.05} for Palatino? The authors of l2tabu or someone else?

Is the factor of +5% just a rule of thumb, or is it the result of some (unknown to me) established typographic formula?

Regarding your first question: I have no idea who was the first to come up with this recommendation. Most likely, though, the need to increase the "leading" when typesetting text in Palatino was "discovered" immediately after people started mixing/matching Palatino and CM.

The +5% recommendation you noted in the l2tabu document can be nothing more than a rule of thumb. My understanding is that it should be understood as a "lower bound" on the required line spread adjustment, rather than as a single number. The code below generates two half-pages of text; the upper half is in Latin Modern, the lower is in Palatino nova with a linespread factor of 1.05. (Both texts are set with nominal font sizes of 10pt, and the text itself is the usual lipsum stuff...) To my eyes at least, the text set in Palatino still has more color than the CM reference text despite the 5% adjustment. Playing with the line spacing setting, I'd say that ca. 7% achieves equal color.

% !TEX TS-program = xelatex
\documentclass[letterpaper,10pt]{article}
\frenchspacing\pagestyle{empty}
\usepackage{fontspec}
\usepackage[margin=1in]{geometry} 
\usepackage{setspace,lipsum}

\begin{document}
\setmainfont{Latin Modern Roman}
\emph{Latin Modern}

\lipsum[1-3]

\vspace{1in}
\setmainfont{Palatino nova Regular}
\setstretch{1.05}
\emph{Palatino, linespread 1.05}

\lipsum[1-3]
\end{document}

enter image description here

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