Font-sizes in figures and subfigures

Question

Assume the following example of two images inside a figure environment

The left image uses font-size 10 and is not scaled. Therefore, the numbers on the axes are of the same size as the Main caption. On the other hand, the right image uses 10pt font-size but has an image-size which would fit over the whole page. Therefore, it is scaled by 0.5. I have two concerns:

• A graphic which ranges over the whole width of the page should maybe use the same font-size which is used in the text. Otherwise numbers maybe look like they are lost.

• For subfigures having a width of approx .45\textwidth the font-size 10pt feels too big. It should be smaller like the caption of the subfigure. The scaled left subfigure has too small numbers IMHO.

Question: Is there a general rule for the font-sizes to use in figures and subfigures? Is it ok to scale the images or should I always create my pdf/eps graphics having the correct final size (and therefore exact font-sizes which match small, footnotesize, scriptsize..)

Additional notes:

I didn't came here unprepared. The first thing I did was skimming through some of my Knuth books. There I noticed, that he uses many different font-sizes in images (at least in the Fascicles of TAOCP), but it always looks kind of coherent.

I thought since there are enough guidelines for good typographic style, there are guidelines for images, diagrams and graphics in books too.

Answer 1

If you want to be perfect, you use in all your graphics the same font (for example libertine) and font size (for example 12 pt) used in your document. So the best would be to prepare all graphics in a way, that they can included in your document without changing, scaling, etc. That has the advantage you can build all your images with the same resolution (for example 600 dpi).

If that is not possible, use the same kind of font (for example with or without serifes) and the same font size (I mean not the number here, I mean that it looks as tall/small as the other font).

If you have to change the fontsize, be not too small (everything, legend and numbers, must be readable!) and do not use a greater font size in your images.

For example with a fontsize of 12 pt in your document I would use as lower fontsize in the graphics 10 pt or 11 pt, not smaller.

If you have to scale your images prepare them (that could mean some trial and error runs ;-)) that they have an optimal font size for legend and numbers in the printed document.

Answer 2

Page 150-167 of the Publication Manual of the American Psychological Association, 6th Edition has a detailed description of how figures should be displayed, and what they should convey. Here are two quotes from the book that should help you:

pg 152-153:

A good figure

• augments rather than duplicates the text,
• is easy to read-its elements (type, lines, labels, symbols, etc.) are large enough to read with ease,
• is consistent with and in the same style as similar figures in the same article ...

Be certain in figures of all types that

• lines are smooth and sharp,
• has typeface that is simple (sans serif) and legible

pg 161:

... Avoid the use of three-dimensional and other effects (including color), except in rare instances in which they demonstrably enhance the presentation of your data. Individual publishers have stated policies with regard to color printing.

Size and proportion of elements. Each element must be large enough and sharp enough to be legible. Use a simple typeface (such as Arial, Futura, or Helvetica) with enough space between letters to avoid crowding. Letters should be clear, sharp, and uniformly dark and should be sized consistently throughout the figure. Type style affects legibility. For example, boldface type tends to thicken and become less readable. The size of lettering should be no smaller than 8 points and no larger than 14 points. As a general guideline, plot symbols should be about the size of a lowercase letter of an average label within the figure. Also consider the weight (i.e., size, density) of each element in a figure in relation to that of every other element, making the most important elements the most prominent. For example, curves on line graphs and outlines of bars on bar graphs should be bolder than axis labels, which should be bolder than the axes and tick marks. Shading. Limit the number of different shadings used in a single graphic. If different shadings are used to distinguish bars or segments of a graph, choose shadings that are distinct (e.g., the best option to distinguish two sets of bars is no shading [open] and black [solid]). If more than three shadings are required, a table may be a better presentation of the data. Use computer-generated art in such a way as to maximize the clarity of the resulting graphic. And as always, keep it simple and clean looking.

So it's best practice to use a sans serif font, since, while serif helps with the reading-flow in body text, it is not as legible as sans serif in figures. I use Calibri for figures and Times Roman for body. You might choose to use CMU Sans Serif in your figures since you use CMU Serif in your body. Font size should be between 8-14 points (as long as it is easy to read). The text mentions nothing about the font size needing to be smaller or equal to the body text.

In the example you provided, a good font size would be between (a) and (b). In (a), the font size makes it unclear which tick each number is associated with on the graph. In (b), the text seems to not be optimally sized for legibility. Assuming your printing this, be sure to check the hardcopy for figure legibility.

The quote above says "consistent with and in the same style as similar figures in the same article". This doesn't mean that the font sizes in all figures should be the same. If a large font is used in a large graph, the same font size would look too large in a small graph (as in (a) from your example).

Final note. You can use

• \the\textwidth to print the width of the body, and
• \the\textheight to print the height of the body

This can help in determining the dimensions of a figure you're producing.

Update: according to a recent conversation in the Tex stackexchange chat, it is more common to use sans serif in figures in the fields of biology and chemistry papers where as the fields of mathematics, physics, and engineering tend to keep the font in figures consistent with the serif font used in the body of the article.