Credit: http://geog.uoregon.edu/geogr/topics/maps01.html

Annual Temperature

library(leaflet)
load('geog495.RData')
pal <- colorQuantile("YlOrRd", NULL, n = 8)
leaflet(orstationc) %>% addTiles() %>%
  addCircleMarkers(~lon, ~lat, color = ~pal(tann))