[R] split a y-axis to show data on different scales

[hadley wickham]

> This is an interesting visual interpretation issue: it may be possible to shade
> the y-axis (which his thick like the top bars in Lattice plots), or shade the
> main graphing area from dark to light (or two shades, for two scales) to give a
> visual idea about the "density" or "stretch" of the space/scale on which the
> points are plotted. There is problems with this as well (interpretation of
> scale), but sometimes it may provide a better and quick visual communication. Is
> this possible in R?

That only emphases that fact that there is a scale break - it does not
solve the problem that the two regions of the graph are fundamentally
non-comparable because they have different scales.  I would argue that
a key component of a statistical graphic (not a pretty picture) is
that scales are consistent throughout the plot.

Hadley