Small Handbook of Information Design:
16 Principles for Better Data Visualizations

523 Information Design I: Data Visualization

Pino Trogu | School of Design | San Francisco State University

2nd edition, July 2013 / This page last updated on September 1, 2021, when the files were moved from online.sfsu.edu/trogu/ to the new host: res.trogu.com/.

Go to principles 1 through 16 below.

Go to companion video part 1 and video part 2.

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Principles

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Every graphic is an ad hoc construction, therefore these rules can be broken depending on the context. However you should try to do the graphic by following these rules first and break them later if necessary.

01 Use pencil and paper
02 Content is first
03 Do not draw graphs by hand
04 Do not enlarge numbers
05 Use words, not just images
06 Use small multiples
07 Do not bungle the meaning
08 Do not create op-art

09 Do not use little dots for numbers
10 Do not use colors (to be memorized)
11 Sort by value, not category
12 Equally space time intervals in timelines
13 Avoid meaningless concept maps
14 You can use small type
15 Do not screen type
16 Psychology of perception

01 Use pencil and paper
In the early and later phases of a project, simply use pencil and paper as your design tools, use graph paper if needed, to sketch ideas, try out designs, and work out your proposal. Work on your ideas and your concepts by sketching your visualizations. Solve problems through sketching by hand, not by staring at a computer screen.
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02 Content is first
Content is first, form is second. Select interesting content. Content-less stuff produces form-less, uninformative visualizations. This means that you need one or more data sets that are rich with data. Many columns and many rows (lots of data points) are better than just two data points. For example, two percentages: 25 and 75 are in themselves not very interesting and it would be hard to pull off an interesting visualization based on just those two numbers.
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03 Do not draw graphs by hand
Do not take a numerical table or spreadsheet and then render the shapes (the bars, the lines) by hand, even if you're using Illustrator. Rather, take the data set and process it through a data visualization program, such as R, Excel, or other. Then bring the file into Illustrator to clean up and fine-tune line weights, typography, color, etc.
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04 Do not enlarge numbers
Do not turn data points into stand-alone enlarged numbers with a percentage sign next to them to make them look important. Filling up your visualization with such "visuals" is not any better, and might in fact be worse, than just having plain text, with no "visualizations" at all. An infographic is not a PowerPoint template. The best thing to do is to combine words and images together.
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NY Times

05 Use words, not just images
Use sentences: subject, verb, object. Close your clauses. Set up an introduction and follow through with visualizations. Use a title, a subtitle, an introduction, main text if needed, labels, captions, credits (for pictures)call-outs, footnotes, sources (for data sets), and a signature (colophon). This is called "the annotation layer". Plus, you can include numerical tables, if needed and appropriate, within the visualization.
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NY Times

06 Use small multiples
Content is king. One single blown-up graphic is not so good, especially if it's just showing very few data points. Don't be stingy. For example, a pie chart showing 25 and 75 percent and filling up a whole poster is not so good. It's much better to have a high number of elements even if they're small, like in a geographic map. Twenty little pies are better than one giant pie. Ten little line graphs are better than a single giant line graph.
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SFSU / DAI AIGA Chapter

07 Do not bungle the meaning
Do not bungle the meaning of your visualization. Say what you mean and do not confuse the reader, starting with your opening title and subtitle. This applies to choice of words as well as pictures. For example, if the topic is "Tuition fee increases" do not say: "Fee hikes on Mount Everest"; say instead: "Fee increases reach new high". If the topic is "Black Friday (shopping)", do not say: "Products cheap as a black sheep"; say instead: "Black Friday keeps more green in your wallet". If the topic is "Christmas shopping", do not say: "Christmas shoppers pray to God for bigger discounts"; say instead: "Consumerism and religion mix in traditional Christmas holiday". Do not play loosely with irony and puns, and don't mix-up your metaphors.
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D. Fernandez

08 Do not create op-art
Do not make op-art (optical art) effects by using bold condensed sans-serif fonts where the strokes are the same width as the counters in the font and also the width of the spacing between the letters. This creates a very annoying, vibrating checkerboard effect. Do not use solid backgrounds, boxes, thick borders, or arbitrary bold type. If you are using solid backgrounds throughout, invert the whole image to see if it's better with the opposite values. On a Mac, use control-option-command-8 to instantly invert the colors of your screen on the computer. See if it would be better the other way around (black type on white background). If nothing is gained by the solid fills, then get rid of them.
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J. Luther, T. Boddy

09 Do not use little dots for numbers
Do not use little dots for percentages. Do not use little people for quantities. Do not visualize quantities by the endless repetition of single units like little dots or little squares. We don't use pebbles to count anymore, and we have invented a tool called "place value". It's better to write out the number or to visualize it using a single solid area, not many tiny areas in little rows. Do not use little people as units to show quantities, even if the quantities represent people. Think of those poor little guys whose limbs get mutilated when you have to represent a fraction: arms, legs, even heads get cut off without mercy!

For more information on this principle, read my article:
Counting But Losing Count: the Legacy of Otto Neurath's Isotype Charts
Visible Language, 52.2, 2018.
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10 Do not use colors (to be memorized)
Do not use colors if the reader has to memorize them. Do not use colors if you have to have a legend for every single color in order to understand the graphic. If no legend is required, then little thinking is needed in order to perceive the graphic. Too many colors in the graph take a huge toll on the attention capacity of the reader. One cannot remember all those colors because we can only remember a small set of things at once: five-seven. Also, colors do not have an intrinsic order, therefore they should not be used to sort things, unless you use value as well: darker color for more, lighter color for less, both being from the same hue or two diverging hues maximum.
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11 Sort by value, not category
Sort by performance (value), not alphabetically. When part of the information is categorical but includes values for each category, do not sort the categories alphabetically. Instead, sort by the values for each of those categories. For example if the categories are products or states and each is a value, sort by the value, not by the alphabetical names of the states or the names of the products.
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timeline
J. Chu

12 Equally space time intervals in timelines
Keep the spacing equal (for equal periods of time) even if that results in big information gaps within certain periods of time. Gaps are as meaningful as periods of concentrated activity. When data is concentrated within a few years, use typography and other means to make everything readable while keeping the temporal spacing even and correct.
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N. Mitchell

13 Avoid meaningless concept maps
Avoid meaningless concept maps and network graphs. For a simple reason: they include on the page too many items and abstract concepts at once. Our working memory (short-term memory) allows us to hold in memory only a few items (4-7) for a very short time (2-4 seconds) before we have to move on. Concept maps look very cool but they are also very uninformative and little information is retained from them in our long-term memory. Generally, the thing one remembers from them is their vague visual form -- the shape of the graph -- rather than the more important subject matter.

For more information on this principle, read my article:
The four-second window: how the time constraint of working memory and other psychological principles determine the success of a graphic design
DRS / Cumulus, 2013
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Use small type
H. Pacheco

14 You can use small type
You can use small type in a big poster. Use as many sizes as needed. A range from 16-18pt to 24pt is the best size range for most text on a poster, excluding the main title and possibly the subtitle, with even smaller sizes for captions and labels. For short texts, use 24pt. Sometimes 30pt for larger text can be used. In general, imagine that you're standing 20 to 30 inches from the poster. At this distance, you should be able to read most text elements in the layout.
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15 Do not screen type
Every font is a wonderful and beautiful universe unto itself. Do we really need to tinker with what is already a very sophisticated sign system? Do not reverse, screen (make tints), border, condense or expand type. Do not italicize type by pressing the "oblique" button. Use a font that already has a wide range of weights. Traditional old-style italic fonts are best to save space if needed, as they are naturally condensed and were designed for this purpose. Do not let your text lines run longer than two-and-a-half times the alphabet -- about 60 characters. Break up the big text boxes into two or more columns whenever necessary so that your measure (box width) is "measured" and correct. Do not justify text if possible, use flush left / ragged right (FL/RR).
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NASA

16 Psychology of perception
Be aware of the following terms related to cognitive psychology and psychology of perception: working memory, chunking, closure, co-construction of meaning, background knowledge, conventions of representation, cultural (visual and verbal) conventions, context, genre, the annotation layer.

For more information about psychology of perception, read my article:
Working memory and background knowledge: Cognitive science in the design classroom
formAkademisk, 8.1, 2015
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Some of these principles are based in part on Edward Tufte's books and workshops. For more info visit: www.edwardtufte.com

Thanks (and apologies) to my students for showing details from their various projects.

Permanent link to this page: res.trogu.com/dataviz/handbook

Pino Trogu Copyright July 2013 - Second edition