r - Add multiple shape legends in ggplot and overlaying shapes - Stack Overflow
ggplot2 point shapes - Easy Guides - Wiki - STHDA
How to Change Point Shape in ggplot2 - Statology
GGPLOT Point Shapes Best Tips - Datanovia
r - Changing shapes used for scale_shape() in ggplot2 - Stack Overflow
Point Shape Options in ggplot - Albert's Blog
Create your own discrete scale — scale_manual • ggplot2
Set guides for each scale — guides • ggplot2
fillable shapes in legend always black · Issue #2322 · tidyverse/ggplot2 · GitHub
Colours and Shapes :: Environmental Computing
Request: support providing shapes as names rather than integers · Issue #2075 · tidyverse/ggplot2 · GitHub
How to use more than 6 shapes in qplot? | ResearchGate
GGPLOT Point Shapes Best Tips - Datanovia
Controlling legend appearance in ggplot2 with override.aes | R-bloggers
GGPLOT Point Shapes Best Tips - Datanovia
star layer for ggplot2
Request: support providing shapes as names rather than integers · Issue #2075 · tidyverse/ggplot2 · GitHub
ggplot2 point shapes - Easy Guides - Wiki - STHDA
r - Assigning 40 shapes or more in scale_shape_manual - Stack Overflow
Plotting Many Groups With ggplot2
