Current learning objective

• -Create basic plots using ggplot2
• -Understand the concept of the grammar of graphics
• Construct plots with multiple layers in ggplot2
• -Adjust scales and guides within ggplot2

Layering plots

Inheriting data and mapping

• A layer inherits the data and mapping from the initialised ggplot object by default

Layer-specific data and aesthetic mapping

• For each layer, aesthetic and/or data can be overwritten.

Illustrative data 🚜 Iowa farmland values by county

Layer specific aesthetic

Layer specific data

Layer specific data as a function of inherited data

Annotation layer

• annotate() allows you to add elements to plots without a data.frame

Summary

• You can construct plots with multiple layers in ggplot2.
• The order of the layer matters.

• A layer inherits the data and mapping from the initialised ggplot object by default
• But the data and mappings for each layer can be overwritten.