Coloring Geographical Maps in R

General
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I am working with the R programming language.

I made the following map:

library(sf)  
library(leaflet)
library(leafgl)
library(colourvalues)
library(leaflet.extras)


nc <- st_read(system.file("gpkg/nc.gpkg", package="sf"), quiet = TRUE) %>% 
  st_transform(st_crs(4326)) %>% 
  st_cast('POLYGON')

leaflet(data = nc) %>% addPolygons( stroke = FALSE) %>% addTiles(group = "OSM") %>%  addProviderTiles(provider = providers$OpenStreetMap) %>% addPolygons(data = nc, weight=1, popup = ~NAME,
                label = ~NAME, group = "name", col = 'blue') %>% 
    addSearchFeatures(targetGroups  = 'name', options = searchFeaturesOptions(zoom=10, openPopup=TRUE))

image
image958×466 202 KB

I wanted to color the polygons different colors so that they are a bit easier to see - I did this by randomly assigning colors to the polygons:

nc$color <- sample(c("red", "blue", "green", "yellow", "purple"), nrow(nc), replace = TRUE)

leaflet(data = nc) %>% 
    addTiles(group = "OSM") %>% 
    addProviderTiles(provider = providers$OpenStreetMap) %>% 
    addPolygons(data = nc, weight=1, popup = ~NAME,
                label = ~NAME, group = "name", fillColor = ~color, fillOpacity = 0.5) %>% 
    addSearchFeatures(targetGroups  = 'name', options = searchFeaturesOptions(zoom=10, openPopup=TRUE))

image
image916×478 211 KB

My Question: Taking inspiration from this famous computer science problem Four color theorem - Wikipedia, I would like to randomly color the polygons in such a way that no bordering polygons have the same color.

I think that I first need to convert the shapefile/map into a network graph:

library(igraph)
adj <- st_touches(nc, sparse = TRUE)
g <- graph_from_adjacency_matrix(as.matrix(adj))
plot(g)

I am not sure how to continue this problem - currently, I thought of an indirect method where I simply choose many different random colors to decrease the odds of two polygons having the same color, but I am interested in learning about new and creative ways to solve my original problem.

Can someone please show me how to do this?

Thanks!

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