Beyond color: Symbols

Using both color and shape to encode a categorical variable can be a useful strategy to reveal relationships more effectively. This double-encoding strategy uses two pre-attentive visual cues to more-quickly communicate information to the reader. This idea is implemented by default in plotly; if you map a variable to the symbol, plotly automatically maps the variable to the color.

To map a variable to the plotting shape, add a symbol argument to the plot_ly() command.

Caution: It is poor practice to use color and shape to communicate different variables, since the two features have been shown to interfere with each other, making it more difficult to distinguish either variable.