Shape scales from Cleveland "Elements of Graphing Data"
scale_shape_cleveland(overlap = TRUE, ...)logical Use the scale for overlapping points?
common discrete scale parameters: name, breaks,
labels, na.value, limits and guide. See
discrete_scale for more details
Cleveland WS. The Elements of Graphing Data. Revised Edition. Hobart Press, Summit, NJ, 1994, pp. 154-164, 234-239.
cleveland_shape_pal for a description of the palette.
Other shapes: circlefill_shape_pal,
cleveland_shape_pal,
scale_shape_circlefill,
scale_shape_tremmel,
tremmel_shape_pal