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[plotting] first explain plotting, then give advice on good plots

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plotting/lecture/plotting.tex
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@ -11,123 +11,6 @@ results.
severe.}{\url{www.xkcd.com}}\label{xkcdplotting}
\end{figure}
\section{What makes a good plot?}
Plot should help/enable the interested reader to get a grasp of the
data and to understand the performed analysis and to critically assess
the presented results. The most important rule is the correct and
complete annotation of the plots. This starts with axis labels and
units and and extends to legends. Incomplete annotation can have
terrible consequences (\figref{xkcdplotting}).
The principle of \emph{ink minimization} may be used a a guiding
principle for appealing plots. It requires that the relation of amount
of ink spent on the data and that spent on other parts of the plot
should be strongly in favor of the data. Ornamental of otherwise
unnecessary gimicks should not be used in scientific contexts. An
exception can be made if the particular figure was designed for
didactic purposes and sometimes for presentations.
\begin{important}[Correct labeling of plots]
A data plot must be sufficiently labeled:
\begin{itemize}
\item Every axis must have a label and the correct unit, if it has
one.\\ (e.g. \code[xlabel()]{xlabel('Speed [m/s]'}).
\item When more than one line is plotted, they have to be labeled
using the figure legend, or similar \matlabfun{legend()}.
\item If using subplots that show similar information on the axes,
they should be scaled to show the same ranges to ease comparison
between plots. (e.g. \code[xlim()]{xlim([0 100])}.\\ If one
chooses to ignore this rule one should explicitly state this in
the figure caption and/or the descriptions in the text.
\item Labels must be large enough to be readable. In particular,
when using the figure in a presentation use large enough fonts.
\end{itemize}
\end{important}
\section{Things that should be avoided.}
When plotting scientific data we should take great care to avoid
suggestive or misleading presentations. Unnecessary additions and
fancy graphical effects make a plot frivolous and also violate the
\emph{ink minimization principle}. Illustrations in comic style
(\figref{comicexamplefig}) are not suited for scientific data in most
instances. For presentations or didactic purposes, however, using a
comic style may be helpful to indicate that the figure is a mere
sketch and the exact position of the data points is of no importance.
\begin{figure}[t]
\includegraphics[width=0.7\columnwidth]{outlier}\vspace{-3ex}
\titlecaption{Comic-like illustration.}{Obviously not suited to
present scientific data. In didactic or illustrative contexts they
can be helpful to focus on the important
aspects.}\label{comicexamplefig}
\end{figure}
The following figures show examples of misleading or suggestive
presentations of data. Several of the effects have been exaggerated to
make the point. A little more subtlety these methods are employed to
nudge the viewers experience into the desired direction. You can find
more examples on \url{https://en.wikipedia.org/wiki/Misleading_graph}.
\begin{figure}[p]
\includegraphics[width=0.35\textwidth]{misleading_pie}
\hspace{0.05\textwidth}
\includegraphics[width=0.35\textwidth]{sample_pie}
\titlecaption{Perspective distortion influences the perceived
size.}{By changing the perspective of the 3-D illustration the
highlighted segment \textbf{C} gains more weight than it should
have. In the left graph segments \textbf{A} and \textbf{C} appear
very similar. The 2-D plot on the right-hand side shows that this
is an
illusion. \url{https://en.wikipedia.org/wiki/Misleading_graph}}\label{misleadingpiefig}
\end{figure}
\begin{figure}[p]
\includegraphics[width=0.9\textwidth]{plot_scaling.pdf}
\titlecaption{Choosing the figure format and scaling of the axes
influences the perceived strength of a correlation.}{All subplots
show the same data. By choosing a certain figure size we can
pronounce or reduce the perceived strength of the correlation
in the data. Technically all three plots are correct.
}\label{misleadingscalingfig}
\end{figure}
\begin{figure}[p]
\begin{minipage}[t]{0.3\textwidth}
\includegraphics[width=0.8\textwidth]{improperly_scaled_graph}
\end{minipage}
\begin{minipage}[t]{0.3\textwidth}
\includegraphics[width=0.8\textwidth]{comparison_properly_improperly_graph}
\end{minipage}
\begin{minipage}[t]{0.3\textwidth}
\includegraphics[width=0.7\textwidth]{properly_scaled_graph}
\end{minipage}
\titlecaption{Scaling of markers and symbols.} {In these graphs
symbols have been used to illustrate the measurements made in two
categories. The measured value for category \textbf{B} is actually
three times the measured value for category \textbf{A}. In the
left graph the symbol for category \textbf{B} has been scaled to
triple height while maintaining the proportions. This appears just
fair and correct but leads to the effect that the covered surface
is not increased to the 3-fold but the 9-fold (center plot). The
plot on the right shows how it could have been done correctly.
\url{https://en.wikipedia.org/wiki/Misleading_graph}}\label{misleadingsymbolsfig}
\end{figure}
By using perspective effects in 3-D plot the perceived size can be
distorted into the desired direction. While the plot is correct in a
strict sense it is rather suggestive
(\figref{misleadingpiefig}). Similarly the choice of figure size and
proportions can lead to different interpretations of the
data. Stretching the y-extent of a graph leads to a stronger
impression of the correlation in the data. Compressing this axis will
lead to a much weaker perceived correlation
(\figref{misleadingscalingfig}). When using symbols to illustrate a
quantity we have to take care not to overrate of difference due to
symbol scaling (\figref{misleadingsymbolsfig}).
\section{The \matlab{} plotting system}
Plotting data in \matlab{} is rather straight forward for simple line
@ -720,7 +603,122 @@ Lissajous figure. The basic steps are:
movie.}, label=animationlisting, firstline=3, lastline=33,
basicstyle=\ttfamily\scriptsize]{movie_example.m}
\section{What makes a good plot?}
Plot should help/enable the interested reader to get a grasp of the
data and to understand the performed analysis and to critically assess
the presented results. The most important rule is the correct and
complete annotation of the plots. This starts with axis labels and
units and and extends to legends. Incomplete annotation can have
terrible consequences (\figref{xkcdplotting}).
The principle of \emph{ink minimization} may be used a a guiding
principle for appealing plots. It requires that the relation of amount
of ink spent on the data and that spent on other parts of the plot
should be strongly in favor of the data. Ornamental of otherwise
unnecessary gimicks should not be used in scientific contexts. An
exception can be made if the particular figure was designed for
didactic purposes and sometimes for presentations.
\begin{important}[Correct labeling of plots]
A data plot must be sufficiently labeled:
\begin{itemize}
\item Every axis must have a label and the correct unit, if it has
one.\\ (e.g. \code[xlabel()]{xlabel('Speed [m/s]'}).
\item When more than one line is plotted, they have to be labeled
using the figure legend, or similar \matlabfun{legend()}.
\item If using subplots that show similar information on the axes,
they should be scaled to show the same ranges to ease comparison
between plots. (e.g. \code[xlim()]{xlim([0 100])}.\\ If one
chooses to ignore this rule one should explicitly state this in
the figure caption and/or the descriptions in the text.
\item Labels must be large enough to be readable. In particular,
when using the figure in a presentation use large enough fonts.
\end{itemize}
\end{important}
\section{Things that should be avoided.}
When plotting scientific data we should take great care to avoid
suggestive or misleading presentations. Unnecessary additions and
fancy graphical effects make a plot frivolous and also violate the
\emph{ink minimization principle}. Illustrations in comic style
(\figref{comicexamplefig}) are not suited for scientific data in most
instances. For presentations or didactic purposes, however, using a
comic style may be helpful to indicate that the figure is a mere
sketch and the exact position of the data points is of no importance.
\begin{figure}[t]
\includegraphics[width=0.7\columnwidth]{outlier}\vspace{-3ex}
\titlecaption{Comic-like illustration.}{Obviously not suited to
present scientific data. In didactic or illustrative contexts they
can be helpful to focus on the important
aspects.}\label{comicexamplefig}
\end{figure}
The following figures show examples of misleading or suggestive
presentations of data. Several of the effects have been exaggerated to
make the point. A little more subtlety these methods are employed to
nudge the viewers experience into the desired direction. You can find
more examples on \url{https://en.wikipedia.org/wiki/Misleading_graph}.
\begin{figure}[p]
\includegraphics[width=0.35\textwidth]{misleading_pie}
\hspace{0.05\textwidth}
\includegraphics[width=0.35\textwidth]{sample_pie}
\titlecaption{Perspective distortion influences the perceived
size.}{By changing the perspective of the 3-D illustration the
highlighted segment \textbf{C} gains more weight than it should
have. In the left graph segments \textbf{A} and \textbf{C} appear
very similar. The 2-D plot on the right-hand side shows that this
is an
illusion. \url{https://en.wikipedia.org/wiki/Misleading_graph}}\label{misleadingpiefig}
\end{figure}
\begin{figure}[p]
\includegraphics[width=0.9\textwidth]{plot_scaling.pdf}
\titlecaption{Choosing the figure format and scaling of the axes
influences the perceived strength of a correlation.}{All subplots
show the same data. By choosing a certain figure size we can
pronounce or reduce the perceived strength of the correlation
in the data. Technically all three plots are correct.
}\label{misleadingscalingfig}
\end{figure}
\begin{figure}[p]
\begin{minipage}[t]{0.3\textwidth}
\includegraphics[width=0.8\textwidth]{improperly_scaled_graph}
\end{minipage}
\begin{minipage}[t]{0.3\textwidth}
\includegraphics[width=0.8\textwidth]{comparison_properly_improperly_graph}
\end{minipage}
\begin{minipage}[t]{0.3\textwidth}
\includegraphics[width=0.7\textwidth]{properly_scaled_graph}
\end{minipage}
\titlecaption{Scaling of markers and symbols.} {In these graphs
symbols have been used to illustrate the measurements made in two
categories. The measured value for category \textbf{B} is actually
three times the measured value for category \textbf{A}. In the
left graph the symbol for category \textbf{B} has been scaled to
triple height while maintaining the proportions. This appears just
fair and correct but leads to the effect that the covered surface
is not increased to the 3-fold but the 9-fold (center plot). The
plot on the right shows how it could have been done correctly.
\url{https://en.wikipedia.org/wiki/Misleading_graph}}\label{misleadingsymbolsfig}
\end{figure}
By using perspective effects in 3-D plot the perceived size can be
distorted into the desired direction. While the plot is correct in a
strict sense it is rather suggestive
(\figref{misleadingpiefig}). Similarly the choice of figure size and
proportions can lead to different interpretations of the
data. Stretching the y-extent of a graph leads to a stronger
impression of the correlation in the data. Compressing this axis will
lead to a much weaker perceived correlation
(\figref{misleadingscalingfig}). When using symbols to illustrate a
quantity we have to take care not to overrate of difference due to
symbol scaling (\figref{misleadingsymbolsfig}).
\section{Summary}
A good plot of scientific data displays the data completely and