title: How to control ggplot's plotting area proportions instead of fitting them to devices in R?
body: <p>By default, each plot in <code>ggplot</code> fits its device.</p>
  
  <p>That's not always desirable. For instance, one may need to make tiles in <code>geom_tile</code> to be squares. Once you change the device or change the number of elements on x/y-axis, the tiles are no longer squares.</p>
  
  <p>Is it possible to set hard proportions or size for a plot and fit the plot in its device's window (or make the device width and height proportional to those of the plot)?</p>