By A Mystery Man Writer
Remove lines from inside a polygon (shapefile) in r - Geographic Information Systems Stack Exchange
r - color polygon boundaries by factor - Stack Overflow
Only a part of the shapefile plotted with ggplot2 in R - Geographic Information Systems Stack Exchange
r - Colour the background of a ggplot polygon to match the lower value of the contour layer - Stack Overflow
Making Maps with R - GeeksforGeeks
Is there a way to zoom in on a mapped polygon (SpatialPolygonsDataFrame) in R (ggplot) without it disappearing? - Geographic Information Systems Stack Exchange
Chapter 14 Graphing Part II STA 444/5 - Introductory Data Science using R
Chapter 7 Map R Gallery Book
Making Maps With R · Reproducible Research.
Chapter 3 Data Visualization Exploring Data Science with R and the Tidyverse: A Concise Introduction