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