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!
The leaflet R package can be installed from CRAN by running:
install.packages("leaflet")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()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])## Warning: Unknown or uninitialised column: `vernacularName`.## 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$label
)Nice! but it is a bit cluttered, we can add clustering by specifying the clusterOptions argument to try and solve this issue:
base %>%
addMarkers(
lng = euc$decimalLongitude, lat = euc$decimalLatitude,
clusterOptions = markerClusterOptions(),
label = euc$label
)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$name)addMeasure() adds a ruler and an area estimator control to the mapaddProviderTiles() Other tiles (base maps) can be added by using this function. Try out: leaflet() %>% addProviderTiles(provider = providers$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!