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diff --git a/Master/texmf-dist/doc/generic/pgf/text-en/pgfmanual-en-guidelines.tex b/Master/texmf-dist/doc/generic/pgf/text-en/pgfmanual-en-guidelines.tex new file mode 100644 index 00000000000..06088165c75 --- /dev/null +++ b/Master/texmf-dist/doc/generic/pgf/text-en/pgfmanual-en-guidelines.tex @@ -0,0 +1,771 @@ +% $Header: /cvsroot/pgf/pgf/doc/pgf/text-en/pgfmanual-en-guidelines.tex,v 1.1 2005/09/02 16:05:42 tantau Exp $ + +% Copyright 2005 by Till Tantau <tantau@cs.tu-berlin.de>. +% +% This program can be redistributed and/or modified under the terms +% of the GNU Public License, version 2. + + + +\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. + + + + +\subsection{Should You Follow 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 questions, because there are good reasons not to follow +general guidelines. +\begin{itemize} +\item + The person who setup 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 setup to address a specific + situation. If you are not in this situation, following a guideline + can do more harm than good. +\item + 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 is + ignorance.'' + + When you are aware of a rule and when you decide that breaking the + rule has a desirable effect, break the rule. +\item + Some guidelines are simply \emph{wrong}, but everyone follows them + out of tradition or is forced to do so. My favorite example is a + guideline a software company I used to work for has set in a big + project: All programmers had to declare the parameters of functions + in \emph{increasing order of size}. So, one-byte + parameters should come first, then two-byte parameters, and so on. + + This guideline is total nonsense. An (arguably) sensible guideline + is ``parameters must be declared alphabetically'' so that parameters + are easier to find. Another (arguably) sensible guideline is + ``parameters must be declared in decreasing order of size'' so that + less byte-alignment cache misses occur when the stack is + accessed. The guideline the company used maximized cache misses and + resulted in a more or less random ordering so that programmers + constantly had to look up the parameter ordering. +\end{itemize} + +So, before you apply a guideline or choose not to apply it, ask +yourself these questions: +\begin{enumerate} +\item + Does this guideline really address my situation? +\item + If you do the opposite a guideline says you should do, will the + advantages outweigh the disadvantages this guideline was supposed to + prevent? +\end{enumerate} + + + +\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. +\item + Arguably, the creation of graphics deserves \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 standalone ``figures.'' Since printers (the +people) like to have their pages ``filled,'' (both for aesthetic and +economic reasons) standalone figures may traditionally be placed on +pages in the document far removed 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 standalone 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 standalone figures: +\begin{itemize} +\item + Standalone 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 +graphic 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 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 the +following: +\begin{itemize} +\item + Are there enough data points to merit a plot? +\end{itemize} + +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: + +\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 where 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 +nearly 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. It 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[text centered,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 very +similar. + +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.'' + +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 + Due 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 our normal 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 loose 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 seldom add + anything of importance to a graphic. +\item + Cute little cliparts can easily draw attention away from the + data. +\end{itemize} + |