title: Relative and absolute font sizes in R: Mixing native and ggplot2 methods
body: <p>The <code>ggplot()</code> function and anything built on top of it ignores the global point size. Functions like <code>plot()</code> and <code>text()</code>, however, do not. The former functions expect font sizes to be specified in absolute terms, through a <code>size</code> parameter, while the latter work with <code>cex</code>, which does relative scaling.</p>
  
  <p>It's not always possible to avoid mixing those mechanisms. Here's an example: You want to plot a series of polygons and place labels inside them, typically for a map. Especially for highly nonconvex polygons, you might want to use <code>rgeos::polygonsLabel()</code> (rather than, say, <code>coordinates()</code>) to determine appropriate label positions. This function is built on top of <code>text()</code> and thus, again, only allows you to pass relative font sizes. But maybe you later want to place the labels with <code>geom_text()</code> from the ggplot2 package; for optimal utility of the <code>rgeos::polygonsLabel()</code> output, font sizes need to match here.</p>