Drawing Maps in R

ggplot2

The map border can be drawn by borders(). Let’s look at an example of USA map:

library(ggplot2)
library(maps)
ggplot() +
  borders("state")

How to add some shapes into the map? If you are familiar with ggplot2, it would be very easy.

Us.cities provides population and location informations of U.S. cities.

data(us.cities)
knitr::kable(head(us.cities))

Us.cities is dataset of cities of USA. When we draw a map, we need

Now we want to mark cities with population more than 500,000 in the map:

us.cities <- subset(us.cities, pop > 500000)
ggplot(us.cities, aes(x = long, y = lat)) +
  geom_point()+
  borders("state")

Of course we can make colour represent population size:

us.cities <- subset(us.cities, pop > 500000)
ggplot(us.cities, aes(x = long, y = lat)) +
  geom_point(aes(color = pop))+
  borders("state")

If you are not so satisfied with the Coordinate ratio, then:

library(mapproj)
ggplot(us.cities, aes(x = long, y = lat)) +
  geom_point(aes(color = pop))+
  borders("state")+
  coord_map()

It is super suitable for a quick look at data map.

Leaflet

Leaflet is a very popular tool based on java. It provides R package so that we can also use it.

library(leaflet)
library(widgetframe)
## Loading required package: htmlwidgets

GetURL <- function(service, host = "basemap.nationalmap.gov") {
  sprintf("https://%s/arcgis/services/%s/MapServer/WmsServer", host, service)
}
pal <- colorNumeric(
  palette = colorRampPalette(c("skyblue", "darkblue"))(length(bound$mean)),
  domain = bound$mean
)
map <- leaflet(bound) %>%
  setView(lng = -95, lat = 40, zoom = 4)%>%
  addPolygons(color = ~ pal(mean), weight = 1, smoothFactor = 0.5,
              opacity = 1.0, fillOpacity = 0.5,label = ~htmltools::htmlEscape(paste(huc2, name)),
              highlightOptions = highlightOptions(color = "white", weight = 2,
                                                  bringToFront = TRUE),
              group = "Region")%>%
  addCircleMarkers(data = Siteinfo,
                   lng = ~dec_lon_va,
                   lat = ~dec_lat_va,
                   radius = ~3,
                   stroke = FALSE,
                   fill = TRUE,
                   color = "red",
                   fillOpacity = 0.4,
                   group = "Site"
  )%>%
  addLegend("bottomright",
            pal = pal,
            values = ~mean,
            title = "Mean",
            labFormat = labelFormat(),
            opacity = 1,
            group="Region"
  ) %>%
  addWMSTiles(GetURL("USGSHydroCached"),layers = "0", group = "River")%>%
  addProviderTiles("Esri.WorldImagery",group = "Topography")%>%
  addLayersControl(
    overlayGroups =c("River", "Topography", "Region","Site"),
    options = layersControlOptions(collapsed=FALSE)
  )
frameWidget(map)