In the previous exercises, we added geoms to the plot and explored the idea of layers inheriting the original aesthetic mappings of the canvas. Sometimes, you’ll want individual layers to have their own mappings. For example, what if we wanted the scatterplot layer to classify the points based on a data-driven property? We achieve this by providing an aesthetic mapping for that layer only.

Let’s explore the aesthetic mappings for the geom_point() layer. What if we wanted to color-code the points on the scatterplot based on a property? It’s possible to customize the color by passing in an aes() aesthetic mapping with the color based on a data-driven property. Observe this example:

viz <- ggplot(data=airquality, aes(x=Ozone, y=Temp)) +
       geom_point(aes(color=Month)) + 
       geom_smooth()

The code above would only change the color of the point layer, it would not affect the color of the smooth layer since the aes() aesthetic mapping is passed at the point layer.

Note: You can read about the individual aesthetics available for each geom when you read its documentation. There are some aesthetics shared across geoms and others that are specific to a particular ones.