Leaflet is one of the most popular Javascript libraries for creating interactive maps. The leaflet R package allows you to create your own leaflet maps without needing to know any Javascript!
install.packages("leaflet")Getting started with leaflet is easy. The leaflet() function creates a map widget that you can store in a variable so that you can modify the map later on. You can add features to the map using the pipe operator (%>%) just like in dplyr. The addTiles() function adds mapping data from Open Street Map.
library(leaflet)
my_map <- leaflet() %>%
addTiles()
my_maplibrary(leaflet)
my_map <- my_map %>%
addMarkers(lat=39.2980803, lng=-76.5898801,
popup="Jeff Leek's Office")
my_mapAdding one marker at a time is often not practical if you want to display many markers. If you have a data frame with columns lat and lng you can pipe that data frame into leaflet() to add all the points at once.
set.seed(2016-04-25)
df <- data.frame(lat = runif(20, min = 39.2, max = 39.3),
lng = runif(20, min = -76.6, max = -76.5))
df %>%
leaflet() %>%
addTiles() %>%
addMarkers()The blue markers that leaflet comes packaged with may not be enough depending on what you’re mapping. Thankfully you can make your own markers from .png files.
hopkinsIcon <- makeIcon(
iconUrl = "http://brand.jhu.edu/content/uploads/2014/06/university.shield.small_.blue_.png",
iconWidth = 31*215/230, iconHeight = 31,
iconAnchorX = 31*215/230/2, iconAnchorY = 16
)
hopkinsLatLong <- data.frame(
lat = c(39.2973166, 39.3288851, 39.2906617),
lng = c(-76.5929798, -76.6206598, -76.5469683))
hopkinsLatLong %>%
leaflet() %>%
addTiles() %>%
addMarkers(icon = hopkinsIcon)When adding multiple markers to a map, you may want to add popups for each marker. You can specify a string of plain text for each popup, or you can provide HTML which will be rendered inside of each popup.
hopkinsSites <- c(
"<a href='http://www.jhsph.edu/'>East Baltimore Campus</a>",
"<a href='https://apply.jhu.edu/visit/homewood/'>Homewood Campus</a>",
"<a href='http://www.hopkinsmedicine.org/johns_hopkins_bayview/'>Bayview Medical Center</a>",
"<a href='http://www.peabody.jhu.edu/'>Peabody Institute</a>",
"<a href='http://carey.jhu.edu/'>Carey Business School</a>"
)
hopkinsLatLong %>%
leaflet() %>%
addTiles() %>%
addMarkers(icon = hopkinsIcon, popup = hopkinsSites)Sometimes you might have so many points on a map that it doesn’t make sense to plot every marker. In these situations leaflet allows you to plot clusters of markers using addMarkers(clusterOptions = markerClusterOptions()). When you zoom in to each cluster, the clusters will separate until you can see the individual markers.
df <- data.frame(lat = runif(500, min = 39.25, max = 39.35),
lng = runif(500, min = -76.65, max = -76.55))
df %>%
leaflet() %>%
addTiles() %>%
addMarkers(clusterOptions = markerClusterOptions())Instead of adding markers or clusters you can easily add circle markers using addCircleMarkers().
df <- data.frame(lat = runif(20, min = 39.25, max = 39.35),
lng = runif(20, min = -76.65, max = -76.55))
df %>%
leaflet() %>%
addTiles() %>%
addCircleMarkers()You can draw arbitrary shapes on the maps you create, including circles and squares. The code below draws a map where the circle on each city is proportional to the population of that city.
md_cities <- data.frame(name = c("Baltimore", "Frederick", "Rockville", "Gaithersburg",
"Bowie", "Hagerstown", "Annapolis", "College Park", "Salisbury", "Laurel"),
pop = c(619493, 66169, 62334, 61045, 55232,
39890, 38880, 30587, 30484, 25346),
lat = c(39.2920592, 39.4143921, 39.0840, 39.1434, 39.0068, 39.6418, 38.9784, 38.9897, 38.3607, 39.0993),
lng = c(-76.6077852, -77.4204875, -77.1528, -77.2014, -76.7791, -77.7200, -76.4922, -76.9378, -75.5994, -76.8483))
md_cities %>%
leaflet() %>%
addTiles() %>%
addCircles(weight = 1, radius = sqrt(md_cities$pop) * 30)## Assuming "lng" and "lat" are longitude and latitude, respectivelyYou can add rectangles on leaflet maps as well:
leaflet() %>%
addTiles() %>%
addRectangles(lat1 = 37.3858, lng1 = -122.0595,
lat2 = 37.3890, lng2 = -122.0625)Adding a legend can be useful if you have markers on your map with different colors:
df <- data.frame(lat = runif(20, min = 39.25, max = 39.35),
lng = runif(20, min = -76.65, max = -76.55),
col = sample(c("red", "blue", "green"), 20, replace = TRUE),
stringsAsFactors = FALSE)
df %>%
leaflet() %>%
addTiles() %>%
addCircleMarkers(color = df$col) %>%
addLegend(labels = LETTERS[1:3], colors = c("blue", "red", "green"))For more details about the leaflet package for R visit http://rstudio.github.io/leaflet/.