Missing Legends in ggplot2 and geom_line

Understanding the Legend Not Appearing for ggplot Geom_point Color Aesthetics: Solutions for Missing Values

Reducing Legend Key Labels in ggplot2: A Simple Solution to Simplify Data Visualization

Understanding Plots in R: A Deep Dive into Plotting and Legends

Customizing Legend Linetype for Groups in ggplot2

Understanding ggmap and ggplot2 Maps with Point Legends: A Comprehensive Guide to Creating Informative Geospatial Visualizations