From 6f9e1680085e7bb4d258f6f8116369d122e196e1 Mon Sep 17 00:00:00 2001
From: Norbert Preining <norbert@preining.info>
Date: Mon, 16 Jan 2023 03:03:27 +0000
Subject: CTAN sync 202301160303

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+% 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}
-- 
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