ere are three
options:</p>
<p>If <code>NULL</code>, the default, the data is inherited from the plot
data as specified in the call to <code><a href="https://ggplot2.tidyverse.org/reference/ggplot.html" class="external-link">ggplot()</a></code>.</p>
<p>A <code>data.frame</code>, or other object, will override the plot
data. All objects will be fortified to produce a data frame. See
<code><a href="https://ggplot2.tidyverse.org/reference/fortify.html" class="external-link">fortify()</a></code> for which variab