# Even though geom_tile() is parametrised by middle-x values, it is
# internally converted to xmin, xmax, ymin, ymax parametrisation so the
# positioning still works.
ggplot() +
  geom_tile(aes(x = rnorm(200), y = 0),
            width = 0.2, height = 0.9,
            position = position_disjoint_ranges(extend = 0.1))
Run the code above in your browser using DataLab