More advice about chunk options

communicate-plots.Rmd

@@ -515,29 +515,31 @@ file.remove("my-plot.pdf")
 
 If you don't specify the `width` and `height` they will be taken from dimensions of the current plotting device. For reproducible code, you'll want to specify them.
 
-Generally, however, I think you should be assembling your final reports using knitr and rmarkdown, so I want to focus on the important chunk options that you should know about for graphics.
+Generally, however, I think you should be assembling your final reports using knitr and rmarkdown, so I want to focus on the important chunk options that you should know about for graphics. You can learn more about `ggsave()` in the documentation.
 
 ### Figure sizing
 
-The most challenging chunk options relate to figure sizing. There are five options that you need to be aware of: `fig.width`, `fig.height`, `fig.asp`, `out.width` and `out.height`. Image sizing is challenging because there are two sizes (the size of the figure created by R and the size in which it is inserted in the output document), and multiple ways of specifying the size (height, width, aspect ratio: pick two out of three). 
+The biggest challenge of graphics in RMarkdown is getting your figures the right size and shape. There are five main options that control figure sizing: `fig.width`, `fig.height`, `fig.asp`, `out.width` and `out.height`. Image sizing is challenging because there are two sizes (the size of the figure created by R and the size in which it is inserted in the output document), and multiple ways of specifying the size (height, width, aspect ratio: pick two out of three). 
 
-I only ever use three of the five options.
+I only ever use three of the five options:
+
+* I find it most aesthetically pleasing for plots to have a consistent
+  width. To enforce this I set `fig.width = 6` (6") and `fig.asp = 0.618` 
+  (the golden ratio) in the defaults. Then in individual chunks, I only
+  adjust `fig.asp`.
 
-* I generally find it easier to make plots line up in an aesthetically pleasing 
-  way if I set `fig.width` and `fig.asp` rather than using width and height.
-  I use defaults of `fig.width = 6` and `fig.asp = 0.618` (the golden ratio).
-  
 * I control the output size with `out.width` and set it to a percentage 
-  (of the line width). I default to `out.width = "70%"`  
-  and `fig.align = 'center'`. That seems to give plots room to breath,
-  without taking up too much space.
+  of the line width). I default to `out.width = "70%"`  
+  and `fig.align = 'center'`. That give plots room to breath, without taking 
+  up too much space.
   
-* If I want multiple plots in columns I set (e.g.) 
-  `out.width = "50%", fig.align = "default"`. Depending on what I'm trying
-  to illustrate (e.g. show data or show plot variations), I'll also tweak
-  `fig.width`, see below. 
-  
-If you find that you're having to squint to read the text, it's typically because you've set the `fig.width` to be much larger than its eventual display. For example, the following three plots have `fig.width` of 4, 6, and 8 respectively.
+* To put multiple plots in a single row I set the `out.width` to 
+  `50%` for two plots, `33%` for 3 plots, or `25%` to 4 plots, and set
+  fig.align = "default"`. Depending on what I'm trying to illustrate (e.g. 
+  show data or show plot variations), I'll also tweak `fig.width`, as 
+  discussed below. 
+
+If you find that you're having to squint to read the text in your plot, you need to tweak `fig.width`. If `fig.width` is larger than the size the figure is rendered in the final doc, the text will be too small; if `fig.width` is smaller, the text will be too big. You'll often need to do a little experimentation to figure out the right ratio between the `fig.width` and the eventual width in your document. To illustrate the principle, the following three plots have `fig.width` of 4, 6, and 8 respectively:
 
 ```{r, include = FALSE}
 plot <- ggplot(mpg, aes(displ, hwy)) + geom_point()
@@ -552,13 +554,15 @@ plot
 plot
 ```
 
-You'll often need to do a little experimentation to figure out the right ratio between the `fig.width` and the eventual width in your document.
+If you want to make sure the font size is the same in all your figures, whenever you set `out.width`, you'll also need to adjust `fig.width` to maintain the same ratio with your default `out.width`. For example, if your default `fig.width` is 6 and `out.width` is 0.7, when you set `out.width = "50%"` you'll need to set `fig.width` to 4.2 (6 * 0.5 / 0.7). 
 
-### Other tips
+### Other important options
 
-When mingling code and text, like I do in this book, I recommend setting `fig.show = "hold"` so that all the plot come after the code. This has the pleasant side effect of forcing you to break up large blocks of code with their explanations.
+When mingling code and text, like I do in this book, I recommend setting `fig.show = "hold"` so that that plots are shown after the code. This has the pleasant side effect of forcing you to break up large blocks of code with their explanations.
 
-If you're producing pdf output, the default graphics type is PDF. This a good default because PDFs are high quality vector graphics. However, that can produce very large and very slow plots if you are displaying thousands of points. In that case, set `dev = "png"` to force the use of PNGs. They are slightly lower quality, but will be much smaller.
+To add a caption to the plot, use `fig.cap`. In RMarkdown this will change the figure from inline to "floating".
+
+If you're producing pdf output, the default graphics type is PDF. This a good default because PDFs are high quality vector graphics. However, they can produce very large and slow plots if you are displaying thousands of points. In that case, set `dev = "png"` to force the use of PNGs. They are slightly lower quality, but will be much more compact.
 
 ## Learning more