Making interactive maps in R with leaflet

Being able to produce interactive maps on the fly can greatly speed up exploratory analysis and is a useful tool for displaying data that would be less informative on a static map.

Leaflet is an open source JavaScript library that is used to create interactive maps on websites. In this post we will look at the the leaflet R package and create some cool interactive maps!

Installation

The leaflet R package can be installed from CRAN by running:

install.packages("leaflet")

Basics

Creating a basic interactive map is simple!

library(leaflet)
leaflet() %>% 
  addTiles()

The Leaflet R package has been designed to be used with pipes (%>%), which makes it easy to add layers and controls such as a scale bar and a mini map.

Most of the time however we will have an area or a study site that we are interested in that we want to view:

leaflet() %>% 
  addTiles() %>%
  addScaleBar() %>% 
  setView(lng = 151.2, lat = -33.86, zoom = 10) %>% 
  addMiniMap()

Markers

Lets plot some species occurence data from GBIF using the rgbif package: We will be displaying all eucalypt observations within the Macquarie Marshes region:

## Getting the data
# install.packages('gbif')
library(rgbif)
gbif_query <- occ_search(genusKey = 7493935,
                         geometry = rgbif::gbif_bbox2wkt(minx = 147.8,miny = -30.6,maxx = 147.4,maxy = -31))
euc <- gbif_query$data
euc$label <- paste(euc$name, '|', euc$vernacularName, '|', euc$year, '-', month.abb[euc$month])
## Creating a map
base <- leaflet() %>% 
  addTiles() %>%
  addScaleBar() %>% 
  setView(lat = mean(euc$decimalLatitude), lng = mean(euc$decimalLongitude), zoom = 10)

base %>% addMarkers(lng = euc$decimalLongitude, lat = euc$decimalLatitude,
                    label = euc$label)

Clustering markers

Nice! but it is a bit cluttered, we can add clustering by specifying the clusterOptions argument to try and solve this issue:

base %>% 
  addMarkers(lng = euc$decimalLongitude, lat = euc$decimalLatitude,
             clusterOptions = markerClusterOptions(),
             label = euc$label)

Colouring markers

You can also add circle markers which can have custom colours, and add a legend:

color_function <- colorFactor("RdYlBu", domain = NULL)

base %>% 
  addCircleMarkers(lng = euc$decimalLongitude, lat = euc$decimalLatitude,
                   color = color_function(euc$name),
                   label = euc$label) %>% 
  addLegend(pal = color_function, values = euc$name)

Other stuff to try out!

• addMeasure() adds a ruler and an area estimator control to the map
• addProviderTiles() Other tiles (base maps) can be added by using this function. Try out: leaflet() %>% addProviderTiles(provider = providers$CartoDB) !
• addLayersControl() adds a selector for choosing multiple layers if you have added them.
• addRasterImage() creates an image overlay from raster data!
• addGeoJSON() adds GeoJSON polygons to the interactive map!

Resources:

• RStudios leaflet guide
• rgbif

Author: John Wilshire

Last updated:

## [1] "Thu Oct  4 15:52:42 2018"