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diff --git a/graphics/pgf/base/doc/pgfmanual-en-guidelines.tex b/graphics/pgf/base/doc/pgfmanual-en-guidelines.tex new file mode 100644 index 0000000000..9511d88cd2 --- /dev/null +++ b/graphics/pgf/base/doc/pgfmanual-en-guidelines.tex @@ -0,0 +1,651 @@ +% Copyright 2018 by Till Tantau +% +% This file may be distributed and/or modified +% +% 1. under the LaTeX Project Public License and/or +% 2. under the GNU Free Documentation License. +% +% See the file doc/generic/pgf/licenses/LICENSE for more details. + + +\section{Guidelines on Graphics} + +The present section is not about \pgfname\ or \tikzname, but about general +guidelines and principles concerning the creation of graphics for scientific +presentations, papers, and books. + +The guidelines in this section come from different sources. Many of them are +just what I would like to claim is ``common sense'', some reflect my personal +experience (though, hopefully, not my personal preferences), some come from +books (the bibliography is still missing, sorry) on graphic design and +typography. The most influential source are the brilliant books by Edward +Tufte. While I do not agree with everything written in these books, many of +Tufte's arguments are so convincing that I decided to repeat them in the +following guidelines. + +The first thing you should ask yourself when someone presents a bunch of +guidelines is: Should I really follow these guidelines? This is an important +question, because there are good reasons not to follow general guidelines. The +person who set up the guidelines may have had other objectives than you do. For +example, a guideline might say ``use the color red for emphasis''. While this +guideline makes perfect sense for, say, a presentation using a projector, red +``color'' has the \emph{opposite} effect of ``emphasis'' when printed using a +black-and-white printer. Guidelines were almost always set up to address a +specific situation. If you are not in this situation, following a guideline can +do more harm than good. + +The second thing you should be aware of is the basic rule of typography is: +``Every rule can be broken, as long as you are \emph{aware} that you are +breaking a rule.'' This rule also applies to graphics. Phrased differently, the +basic rule states: ``The only mistakes in typography are things done in +ignorance.'' When you are aware of a rule and when you decide that breaking the +rule has a desirable effect, break the rule. + + +\subsection{Planning the Time Needed for the Creation of Graphics} + +When you create a paper with numerous graphics, the time needed to create these +graphics becomes an important factor. How much time should you calculate for +the creation of graphics? + +As a general rule, assume that a graphic will need as much time to create as +would a text of the same length. For example, when I write a paper, I need +about one hour per page for the first draft. Later, I need between two and four +hours per page for revisions. Thus, I expect to need about half an hour for the +creation of \emph{a first draft} of a half page graphic. Later on, I expect +another one to two hours before the final graphic is finished. + +In many publications, even in good journals, the authors and editors have +obviously invested a lot of time on the text, but seem to have spend about +five minutes to create all of the graphics. Graphics often seem to have been +added as an ``afterthought'' or look like a screen shot of whatever the +authors's statistical software shows them. As will be argued later on, the +graphics that programs like \textsc{gnuplot} produce by default are of poor +quality. + +Creating informative graphics that help the reader and that fit together with +the main text is a difficult, lengthy process. +% +\begin{itemize} + \item Treat graphics as first-class citizens of your papers. They deserve + as much time and energy as the text does. Indeed, the creation of + graphics might deserve \emph{even more} time than the writing of the + main text since more attention will be paid to the graphics and they + will be looked at first. + \item Plan as much time for the creation and revision of a graphic as you + would plan for text of the same size. + \item Difficult graphics with a high information density may require even + more time. + \item Very simple graphics will require less time, but most likely you do + not want to have ``very simple graphics'' in your paper, anyway; just + as you would not like to have a ``very simple text'' of the same + size. +\end{itemize} + + +\subsection{Workflow for Creating a Graphic} + +When you write a (scientific) paper, you will most likely follow the following +pattern: You have some results/ideas that you would like to report about. The +creation of the paper will typically start with compiling a rough outline. +Then, the different sections are filled with text to create a first draft. This +draft is then revised repeatedly until, often after substantial revision, a +final paper results. In a good journal paper there is typically not be a single +sentence that has survived unmodified from the first draft. + +Creating a graphics follows the same pattern: +% +\begin{itemize} + \item Decide on what the graphic should communicate. Make this a + conscious decision, that is, determine ``What is the graphic supposed + to tell the reader?'' + \item Create an ``outline'', that is, the rough overall ``shape'' of the + graphic, containing the most crucial elements. Often, it is useful to + do this using pencil and paper. + \item Fill out the finer details of the graphic to create a first draft. + \item Revise the graphic repeatedly along with the rest of the paper. +\end{itemize} + + +\subsection{Linking Graphics With the Main Text} + +Graphics can be placed at different places in a text. Either, they can be +inlined, meaning they are somewhere ``in the middle of the text'' or they can +be placed in stand-alone ``figures''. Since printers (the people) like to have +their pages ``filled'', (both for aesthetic and economic reasons) stand-alone +figures may traditionally be placed on pages in the document far away from the +main text that refers to them. \LaTeX\ and \TeX\ tend to encourage this +``drifting away'' of graphics for technical reasons. + +When a graphic is inlined, it will more or less automatically be linked with +the main text in the sense that the labels of the graphic will be implicitly +explained by the surrounding text. Also, the main text will typically make it +clear what the graphic is about and what is shown. + +Quite differently, a stand-alone figure will often be viewed at a time when the +main text that this graphic belongs to either has not yet been read or has been +read some time ago. For this reason, you should follow the following guidelines +when creating stand-alone figures: +% +\begin{itemize} + \item Stand-alone figures should have a caption than should make them + ``understandable by themselves''. + + For example, suppose a graphic shows an example of the different + stages of a quicksort algorithm. Then the figure's caption should, at + the very least, inform the reader that ``the figure shows the + different stages of the quicksort algorithm introduced on page xyz''. + and not just ``Quicksort algorithm''. + \item A good caption adds as much context information as possible. For + example, you could say: ``The figure shows the different stages of + the quicksort algorithm introduced on page xyz. In the first line, + the pivot element 5 is chosen. This causes\dots'' While this + information can also be given in the main text, putting it in the + caption will ensure that the context is kept. Do not feel afraid of a + 5-line caption. (Your editor may hate you for this. Consider hating + them back.) + \item Reference the graphic in your main text as in ``for an example of + quicksort `in action', see Figure~2.1 on page xyz''. + \item Most books on style and typography recommend that you do not use + abbreviations as in ``Fig.~2.1'' but write ``Figure~2.1''. + + The main argument against abbreviations is that ``a period is too + valuable to waste it on an abbreviation''. The idea is that a period + will make the reader assume that the sentence ends after ``Fig'' and + it takes a ``conscious backtracking'' to realize that the sentence + did not end after all. + + The argument in favor of abbreviations is that they save space. + + Personally, I am not really convinced by either argument. On the one + hand, I have not yet seen any hard evidence that abbreviations slow + readers down. On the other hand, abbreviating all ``Figure'' by + ``Fig.'' is most unlikely to save even a single line in most documents. + I avoid abbreviations. +\end{itemize} + + +\subsection{Consistency Between Graphics and Text} + +Perhaps the most common ``mistake'' people do when creating graphics (remember +that a ``mistake'' in design is always just ``ignorance'') is to have a +mismatch between the way their graphics look and the way their text looks. + +It is quite common that authors use several different programs for creating the +graphics of a paper. An author might produce some plots using \textsc{gnuplot}, +a diagram using \textsc{xfig}, and include an |.eps| graphic a coauthor +contributed using some unknown program. All these graphics will, most likely, +use different line widths, different fonts, and have different sizes. In +addition, authors often use options like |[height=5cm]| when including graphics +to scale them to some ``nice size''. + +If the same approach were taken to writing the main text, every section would +be written in a different font at a different size. In some sections all +theorems would be underlined, in another they would be printed all in uppercase +letters, and in another in red. In addition, the margins would be different on +each page. Readers and editors would not tolerate a text if it were written in +this fashion, but with graphics they often have to. + +To create consistency between graphics and text, stick to the following +guidelines: +% +\begin{itemize} + \item Do not scale graphics. + + This means that when generating graphics using an external program, + create them ``at the right size''. + \item Use the same font(s) both in graphics and the body text. + \item Use the same line width in text and graphics. + + The ``line width'' for normal text is the width of the stem of letters + like T{}. For \TeX, this is usually $0.4\,\mathrm{pt}$. However, some + journals will not accept graphics with a normal line width below + $0.5\,\mathrm{pt}$. + \item When using colors, use a consistent color coding in the text and in + graphics. For example, if red is supposed to alert the reader to + something in the main text, use red also in graphics for important + parts of the graphic. If blue is used for structural elements like + headlines and section titles, use blue also for structural elements + of your graphic. + + However, graphics may also use a logical intrinsic color + coding. For example, no matter what colors you normally use, readers + will generally assume, say, that the color green as ``positive, go, + ok'' and red as ``alert, warning, action''. +\end{itemize} + +Creating consistency when using different graphic programs is almost +impossible. For this reason, you should consider sticking to a single graphics +program. + + +\subsection{Labels in Graphics} + +Almost all graphics will contain labels, that is, pieces of text that explain +parts of the graphics. When placing labels, stick to the following guidelines: +% +\begin{itemize} + \item Follow the rule of consistency when placing labels. You should do + so in two ways: First, be consistent with the main text, that is, use + the same font as the main text also for labels. Second, be consistent + between labels, that is, if you format some labels in some particular + way, format all labels in this way. + \item In addition to using the same fonts in text and graphics, you + should also use the same notation. For example, if you write $1/2$ in + your main text, also use ``$1/2$'' as labels in graphics, not + ``0.5''. A $\pi$ is a ``$\pi$'' and not ``$3.141$''. Finally, + $\mathrm e^{-\mathrm i \pi}$ is ``$\mathrm e^{-\mathrm i \pi}$'', not + ``$-1$'', let alone ``-1''. + \item Labels should be legible. They should not only have a reasonably + large size, they also should not be obscured by lines or other text. + This also applies to labels of lines and text \emph{behind} the + labels. + \item Labels should be ``in place''. Whenever there is enough space, + labels should be placed next to the thing they label. Only if + necessary, add a (subdued) line from the label to the labeled object. + Try to avoid labels that only reference explanations in external + legends. Reader have to jump back and forth between the explanation and + the object that is described. + \item Consider subduing ``unimportant'' labels using, for example, a gray + color. This will keep the focus on the actual graphic. +\end{itemize} + + +\subsection{Plots and Charts} + +One of the most frequent kind of graphics, especially in scientific papers, are +\emph{plots}. They come in a large variety, including simple line plots, +parametric plots, three dimensional plots, pie charts, and many more. + +Unfortunately, plots are notoriously hard to get right. Partly, the default +settings of programs like \textsc{gnuplot} or Excel are to blame for this since +these programs make it very convenient to create bad plots. + +The first question you should ask yourself when creating a plot is: Are there +enough data points to merit a plot? If the answer is ``not really'', use a +table. + +A typical situation where a plot is unnecessary is when people present a few +numbers in a bar diagram. Here is a real-life example: At the end of a seminar +a lecturer asked the participants for feedback. Of the 50 participants, 30 +returned the feedback form. According to the feedback, three participants +considered the seminar ``very good'', nine considered it ``good'', ten ``ok'', +eight ``bad'', and no one thought that the seminar was ``very bad''. + +A simple way of summing up this information is the following table: + +\medskip +\begin{tabular}{lp{3.75cm}r} + \emph{Rating given} & \raggedright\emph{Participants (out of 50) who gave this rating} & + \emph{Percentage} \\[1.75em] + ``very good'' & \hfil\hphantom{0}3\hfil & \hphantom{0}6\% \\ + ``good'' & \hfil\hphantom{0}9\hfil & 18\% \\ + ``ok'' & \hfil10\hfil & 20\% \\ + ``bad'' & \hfil\hphantom{0}8\hfil & 16\% \\ + ``very bad'' & \hfil\hphantom{0}0\hfil & \hphantom{0}0\% \\[2mm] + none & \hfil20\hfil & 40\% \\ +\end{tabular} + +\bigskip +What the lecturer did was to visualize the data using a 3D bar diagram. It +looked like this (except that in reality the numbers where typeset using some +extremely low-resolution bitmap font and were near-unreadable): + +\bigskip +\par +\begin{tikzpicture}[y=0.03cm,z=3mm] + \foreach \y in {0,20,40,60,80,100} + \draw[dashed] (0,\y,0) node[left] {\y} -- (0,\y,1) -- (6,\y,1); + + \draw (0,0,0) -- (0,100,0) (0,0,1) -- (0,100,1); + \draw (0,0,0) -- (6,0,0); + + \foreach \x/\xtext/\height in {1/very good/10,2/good/30,3/ok/33,4/bad/27,5/very bad/0} + { + \draw (\x,0) node[rotate=90,anchor=east] {\xtext}; + + \begin{scope}[xshift=\x cm] + + \filldraw[fill=blue!50] (-.3,0,0) rectangle (.3,\height,0); + \filldraw[fill=blue!30] (.3,0,0) -- (.3,0,1) -- (.3,\height,1) -- (.3,\height,0) --cycle; + \filldraw[fill=blue!20] (-.3,\height,0) -- (.3,\height,0) -- + (.3,\height,1) -- (-.3,\height,1) --cycle; + \end{scope} + } +\end{tikzpicture} +\bigskip + +Both the table and the ``plot'' have about the same size. If your first thought +is ``the graphic looks nicer than the table'', try to answer the following +questions based on the information in the table or in the graphic: +% +\begin{enumerate} + \item How many participants were there? + \item How many participants returned the feedback form? + \item What percentage of the participants returned the feedback form? + \item How many participants checked ``very good''? + \item What percentage out of all participants checked ``very good''? + \item Did more than a quarter of the participants check ``bad'' or ``very + bad''? + \item What percentage of the participants that returned the form checked + ``very good''? +\end{enumerate} + +Sadly, the graphic does not allow us to answer \emph{a single one of these +questions}. The table answers all of them directly, except for the last one. In +essence, the information density of the graphic is very close to zero. The +table has a much higher information density; despite the fact that it uses +quite a lot of white space to present a few numbers. Here is the list of things +that went wrong with the 3D-bar diagram: +% +\begin{itemize} + \item The whole graphic is dominated by irritating background lines. + \item It is not clear what the numbers at the left mean; presumably + percentages, but it might also be the absolute number of + participants. + \item The labels at the bottom are rotated, making them hard to read. + + (In the real presentation that I saw, the text was rendered at a very + low resolution with about 10 by 6 pixels per letter with wrong + kerning, making the rotated text almost impossible to read.) + \item The third dimension adds complexity to the graphic without adding + information. + \item The three dimensional setup makes it much harder to gauge the + height of the bars correctly. Consider the ``bad'' bar. Is the number + this bar stands for more than 20 or less? While the front of the bar + is below the 20 line, the back of the bar (which counts) is above. + \item It is impossible to tell which numbers are represented by the + bars. Thus, the bars needlessly hide the information these bars are + all about. + \item What do the bar heights add up to? Is it 100\% or 60\%? + \item Does the bar for ``very bad'' represent 0 or~1? + \item Why are the bars blue? +\end{itemize} + +You might argue that in the example the exact numbers are not important for the +graphic. The important things is the ``message'', which is that there are more +``very good'' and ``good'' ratings than ``bad'' and ``very bad''. However, to +convey this message either use a sentence that says so or use a graphic that +conveys this message more clearly: + +\medskip +\par +\begin{tikzpicture} + \colorlet{good}{green!75!black} + \colorlet{bad}{red} + \colorlet{neutral}{black!60} + \colorlet{none}{white} + + \node[align=center,text width=3cm]{Ratings given by 50~participants}; + + \begin{scope}[line width=4mm,rotate=270] + \draw[good] (-123:2cm) arc (-123:-101:2cm); + \draw[good!60!white] (-36:2cm) arc (-36:-101:2cm); + \draw[neutral] (-36:2cm) arc (-36:36:2cm); + \draw[bad!60!white] (36:2cm) arc (36:93:2cm); + + \newcount\mycount + \foreach \angle in {0,72,...,3599} + { + \mycount=\angle\relax + \divide\mycount by 10\relax + \draw[black!15,thick] (\the\mycount:18mm) -- (\the\mycount:22mm); + } + + \draw (0:2.2cm) node[below] {``ok'': 10 (20\%)}; + \draw (165:2.2cm) node[above] {none: 20 (40\%)}; + \draw (-111:2.2cm) node[left] {``very good'': 3 (6\%)}; + \draw (-68:2.2cm) node[left] {``good'': 9 (18\%)}; + \draw (65:2.2cm) node[right] {``bad'': 8 (16\%)}; + \draw (93:2.2cm) node[right] {``very bad'': 0 (0\%)}; + \end{scope} + \draw[gray] (0,0) circle (2.2cm) circle (1.8cm); +\end{tikzpicture} + +\bigskip +The above graphic has about the same information density as the table (about +the same size and the same numbers are shown). In addition, one can directly +``see'' that there are more good or very good ratings than bad ones. One can +also ``see'' that the number of people who gave no rating at all is not +negligible, which is quite common for feedback forms. + +Charts are not always a good idea. Let us look at an example that I redrew from +a pie chart in \emph{Die Zeit}, June 4th, 2005: + +\bigskip +\par +\begin{tikzpicture} + \begin{scope}[xscale=3.2,yscale=1.2] + + \sffamily + \coordinate (right border) at (2.0cm,-1.7cm); + \coordinate (left border) at (-2.5cm,2.1cm); + + \fill[black!25] ([xshift=-2mm,yshift=1.1cm]left border) rectangle ([xshift=2mm,yshift=-.3cm]right border); + + \node[below right,text width=10cm,inner sep=0pt] at ([yshift=.9cm,xshift=-1mm]left border) + { {\color{black!75} \Large Kohle ist am wichtigsten}\\ + Energiemix bei der deutschen Stromerzeugung 2004}; + + \filldraw[draw=gray,fill=white] ([xshift=-1mm]left border) node[below right,black] + {\footnotesize Gesamte Netto-Stromerzeugung in Prozent, in + Milliarden Kilowattstunden (Mrd.\ kWh)} + rectangle ([xshift=1mm]right border); + + % The 3D stuff + \pgfdeclarehorizontalshading{zeit}{100bp} + {color(0pt)=(black); + color(25bp)=(black); + color(37bp)=(white); + color(50bp)=(black); + color(62bp)=(white); + color(75bp)=(black); + color(100bp)=(black)} + + \shadedraw[very thin,shading=zeit,yshift=-1.5mm] (0,0) circle (1cm); + + \fill[green!20!gray] (0,0) -- (90:1cm) arc (90:-5:1cm); + \fill[white!20!gray] (0,0) -- (-5:1cm) arc (-5:-105:1cm); + \fill[orange!20!gray] (0,0) -- (-105:1cm) arc (-105:-180:1cm); + \fill[orange!60!white] (0,0) -- (180:1cm) arc (180:150:1cm); + \fill[black!75!white] (0,0) -- (150:1cm) arc (150:145:1cm); + \fill[blue!90!white] (0,0) -- (145:1cm) arc (145:135:1cm); + \fill[blue!50!white] (0,0) -- (135:1cm) arc (135:92:1cm); + \fill[yellow!50!black] (0,0) -- (92:1cm) arc (92:90:1cm); + + \begin{scope}[very thin] + \draw (0,0) -- (90:1cm); + \draw (0,0) -- (-5:1cm); + \draw (0,0) -- (-105:1cm); + \draw (0,0) -- (-180:1cm); + \draw (0,0) -- (150:1cm); + \draw (0,0) -- (145:1cm); + \draw (0,0) -- (135:1cm); + \draw (0,0) -- (92:1cm); + + \draw(0,0) circle (1cm); + \end{scope} + + \node (Regenerative) at (115:.75cm) {\bfseries 9,4\%}; + \node (Kernenergie) at (30:.5cm) {\bfseries 27,8\%}; + \node (Braunkohle) at (-45:.6cm) {\bfseries 25,6\%}; + \node (Steinkohle) at (-135:.6cm) {\bfseries 22,3\%}; + \node (Erdgas) at (168:.75cm) {\bfseries 10,4\%}; + \coordinate (Mineral) at (147:.9cm); + \coordinate (Sonstige) at (140:.9cm); + + \small + \draw (Regenerative.north) |- ([yshift=.25cm]Regenerative.north -| right border) coordinate (Regenerative label); + \draw (91:.9cm) |- (Regenerative label); + \node[above left] at (Regenerative label) {Regenerative\ + {\footnotesize (53,7 kWh)/davon} Wind \textbf{4,4\%} \footnotesize (25,0 kWh)}; + + \draw (Kernenergie.base east) -- (Kernenergie.base east -| right border) coordinate (Kernenergie label); + \node[above left] at (Kernenergie label) {Kernenergie}; + \node[below left] at (Kernenergie label) {\footnotesize (158,4 kWh)}; + + \draw (Braunkohle.south) |- ([yshift=-.75cm]Braunkohle.south -| right border) coordinate (Braunkohle label); + \node[above left] at (Braunkohle label) {Braunkohle\ \ \footnotesize (146,0 kWh)}; + + \draw (Steinkohle.south) |- ([yshift=-.75cm]Steinkohle.south -| left border) coordinate (Steinkohle label); + \node[above right] at (Steinkohle label) {Steinkohle\ \ \footnotesize (127,1 kWh)}; + + \draw (Erdgas.base west) -- (Erdgas.base west -| left border) coordinate (Erdgas label); + \node[above right] at (Erdgas label) {Erdgas\ \ \footnotesize (59,2 kWh)}; + + \draw (Mineral) -- (Mineral -| left border) coordinate (Mineral label); + \node[above right] at (Mineral label) {Mineral\"olprodukte\ \ + \footnotesize (9,2 kWh) \ \ \normalsize\textbf{1,6\%}}; + + \draw (Sonstige) |- (Regenerative label -| left border) coordinate (Sonstige label); + \node[above right] at (Sonstige label) {Sonstige\ \ + \footnotesize (16,5 kWh) \hskip1.5cm\ + \normalsize\textbf{2,9\%}}; + \end{scope} +\end{tikzpicture} + +This graphic has been redrawn in \tikzname, but the original looks almost +exactly the same. + +At first sight, the graphic looks ``nice and informative'', but there are a lot +of things that went wrong: +% +\begin{itemize} + \item The chart is three dimensional. However, the shadings add nothing + ``information-wise'', at best, they distract. + \item In a 3D-pie-chart the relative sizes are very strongly distorted. + For example, the area taken up by the gray color of ``Braunkohle'' is + larger than the area taken up by the green color of ``Kernenergie'' + \emph{despite the fact that the percentage of Braunkohle is less than + the percentage of Kernenergie}. + \item The 3D-distortion gets worse for small areas. The area of + ``Regenerative'' somewhat larger than the area of ``Erdgas''. The + area of ``Wind'' is slightly smaller than the area of + ``Mineral\"olprodukte'' \emph{although the percentage of Wind is + nearly three times larger than the percentage of + Mineral\"olprodukte.} + + In the last case, the different sizes are only partly due to + distortion. The designer(s) of the original graphic have also made + the ``Wind'' slice too small, even taking distortion into + account. (Just compare the size of ``Wind'' to ``Regenerative'' in + general.) + \item According to its caption, this chart is supposed to inform us that + coal was the most important energy source in Germany in 2004. + Ignoring the strong distortions caused by the superfluous and + misleading 3D-setup, it takes quite a while for this message to get + across. + + Coal as an energy source is split up into two slices: one for + ``Steinkohle'' and one for ``Braunkohle'' (two different kinds of + coal). When you add them up, you see that the whole lower half of + the pie chart is taken up by coal. + + The two areas for the different kinds of coal are not visually + linked at all. Rather, two different colors are used, the labels are + on different sides of the graphic. By comparison, ``Regenerative'' + and ``Wind'' are very closely linked. + \item The color coding of the graphic follows no logical pattern at all. + Why is nuclear energy green? Regenerative energy is light blue, + ``other sources'' are blue. It seems more like a joke that the area + for ``Braunkohle'' (which literally translates to ``brown coal'') is + stone gray, while the area for ``Steinkohle'' (which literally + translates to ``stone coal'') is brown. + \item The area with the lightest color is used for ``Erdgas''. This area + stands out most because of the brighter color. However, for this + chart ``Erdgas'' is not really important at all. +\end{itemize} +% +Edward Tufte calls graphics like the above ``chart junk''. (I am happy to +announce, however, that \emph{Die Zeit} has stopped using 3D pie charts and +their information graphics have got somewhat better.) + +Here are a few recommendations that may help you avoid producing chart junk: +% +\begin{itemize} + \item Do not use 3D pie charts. They are \emph{evil}. + \item Consider using a table instead of a pie chart. + \item Do not apply colors randomly; use them to direct the readers's + focus and to group things. + \item Do not use background patterns, like a crosshatch or diagonal + lines, instead of colors. They distract. Background patterns in + information graphics are \emph{evil}. +\end{itemize} + + +\subsection{Attention and Distraction} + +Pick up your favorite fiction novel and have a look at a typical page. You will +notice that the page is very uniform. Nothing is there to distract the reader +while reading; no large headlines, no bold text, no large white areas. Indeed, +even when the author does wish to emphasize something, this is done using +italic letters. Such letters blend nicely with the main text -- at a distance +you will not be able to tell whether a page contains italic letters, but you +would notice a single bold word immediately. The reason novels are typeset this +way is the following paradigm: Avoid distractions. + +Good typography (like good organization) is something you do \emph{not} notice. +The job of typography is to make reading the text, that is, ``absorbing'' its +information content, as effortless as possible. For a novel, readers absorb the +content by reading the text line-by-line, as if they were listening to someone +telling the story. In this situation anything on the page that distracts the +eye from going quickly and evenly from line to line will make the text harder +to read. + +Now, pick up your favorite weekly magazine or newspaper and have a look at a +typical page. You will notice that there is quite a lot ``going on'' on the +page. Fonts are used at different sizes and in different arrangements, the text +is organized in narrow columns, typically interleaved with pictures. The reason +magazines are typeset in this way is another paradigm: Steer attention. + +Readers will not read a magazine like a novel. Instead of reading a magazine +line-by-line, we use headlines and short abstracts to check whether we want to +read a certain article or not. The job of typography is to steer our attention +to these abstracts and headlines, first. Once we have decided that we want to +read an article, however, we no longer tolerate distractions, which is why the +main text of articles is typeset exactly the same way as a novel. + +The two principles ``avoid distractions'' and ``steer attention'' also apply to +graphics. When you design a graphic, you should eliminate everything that will +``distract the eye''. At the same time, you should try to actively help the +reader ``through the graphic'' by using fonts/colors/line widths to highlight +different parts. + +Here is a non-exhaustive list of things that can distract readers: +% +\begin{itemize} + \item Strong contrasts will always be registered first by the eye. For + example, consider the following two grids: + + \medskip\par + \begin{tikzpicture}[x=40pt,y=40pt] + \draw[step=10pt,gray] (0,0) grid +(1,1); + \draw[step=2pt] (2,0) grid +(1,1); + \end{tikzpicture} + + \medskip + Even though the left grid comes first in English reading order, the + right one is much more likely to be seen first: The white-to-black + contrast is higher than the gray-to-white contrast. In addition, + there are more ``places'' adding to the overall contrast in the right + grid. + + Things like grids and, more generally, help lines usually should not + grab the attention of the readers and, hence, should be typeset with + a low contrast to the background. Also, a loosely-spaced grid is less + distracting than a very closely-spaced grid. + \item Dashed lines create many points at which there is black-to-white + contrast. Dashed or dotted lines can be very distracting and, hence, + should be avoided in general. + + Do not use different dashing patterns to differentiate curves in + plots. You lose data points this way and the eye is not particularly + good at ``grouping things according to a dashing pattern''. The eye + is \emph{much} better at grouping things according to colors. + \item Background patterns filling an area using diagonal lines or + horizontal and vertical lines or just dots are almost always + distracting and, usually, serve no real purpose. + \item Background images and shadings distract and only seldomly add + anything of importance to a graphic. + \item Cute little clip arts can easily draw attention away from the data. +\end{itemize} |