It’s super-simple to use the Project Linework maps with the leaflet htmlwidget See more here: https://github.com/hrbrmstr/lineworkmaps

# devtools::install_github("hrbrmstr/lineworkmaps")
library(lineworkmaps)
library(leaflet)

Elmer Casual CONUS

elmer <- linework_map("elmer_casual")
elmer_conus <- elmer[elmer$COUNTRY=="US" & elmer$Name != "Alaska",]
leaflet() %>% addPolygons(data=elmer_conus, weight=1)

Charmingly Inaccurate CONUS

charming_conus <- linework_map("charmingly_inaccurate")
leaflet() %>% addPolygons(data=charming_conus, weight=1)

Geo-Metro CONUS

geo_metro <- linework_map("geo_metro")
geo_metro_conus <- geo_metro[geo_metro$COUNTRY=="US" & geo_metro$NAME != "Alaska",]
leaflet() %>% addPolygons(data=geo_metro_conus, weight=1)

Times Approximate CONUS

times_conus <- linework_map("times_approximate")
leaflet() %>% addPolygons(data=times_conus, weight=1)

Twenty Seventy CONUS

twenty <- linework_map("twenty_seventy")
twenty_conus <- twenty[twenty$Country=="US" & !twenty$Name %in% c("Alaska"),]
leaflet() %>% addPolygons(data=twenty_conus, weight=1)

Wargames CONUS

wargames <- linework_map("wargames")
wargames_conus <- wargames[wargames$iso_a2=="US" & !wargames$code_hasc %in% c("US.HI", "US.AK"),]
leaflet() %>% addPolygons(data=wargames_conus, weight=1)