Instruction: Describe how you would create a complex, multi-layered visualization using ggplot2. Consider a dataset containing temporal data with multiple groups and categories.
Context: The candidate needs to demonstrate deep understanding of ggplot2 and its layering system, including how to manipulate aesthetics, facets, and scales to reveal insights in complex datasets. The answer should cover the use of various ggplot2 components and how they can be combined to handle sophisticated visualization tasks.