Geospatial maps with leaflet

Building Dashboards with shinydashboard

Png Kee Seng

Researcher

The structure of a leaflet plot

The first layer required is leaflet()
- Like ggplot()
addTiles() adds the world map
- Like x, y in ggplot
New layers are added using %>%
- Like + in ggplot

library(leaflet)

m <- leaflet() %>%

  addTiles()

A blank leaflet canvas.

A leaflet canvas with the world map.

Different map providers

Add addProviderTiles()
Some examples of providers are
- MtbMap: Mountain biking
- Esri.NatGeoWorldMap: By National Geo
- Stamen.Toner: Black and white

m %>%
  addProviderTiles(providers$MtbMap)

m %>%
  addProviderTiles(providers$Esri.NatGeoWorldMap)

m %>% 
  addProviderTiles(providers$Stamen.Toner)

Leaflet with MtbMap provider.

Leaflet with nat geo provider.

Leaflet with stamen toner provider.

¹ https://rstudio.github.io/leaflet/basemaps.html

Adding polygons in leaflet

Add polygons using addPolygon()
- The main argument required is a sf object

Adding a polygon in leaflet.

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

  addPolygons(data=london_poly,

              col="red",

              label=~Name)

Adding polylines in leaflet

Need longitudes and latitudes
- Contained in $geometry[[1]]
Polylines are plotted using addPolylines()
- Longitudes and latitudes correspond to first and second columns

loop_geo <- london_loop$geometry[[1]]

capital_geo <- london_capital$geometry[[1]]

m2 <- leaflet() %>% 
  addTiles() %>% 
  addPolygons(data = london_poly, col="red", 
                  label=~Name) %>% 

  addPolylines(loop_geo[,1], loop_geo[,2]) %>%
  addPolylines(capital_geo[,1], capital_geo[,2],
               color = "orange")

Adding markers in leaflet

Can add markers
- addCircleMarkers(): represents each point by a circle
- addMarkers(): represents each point by a regular marker

m2 %>%
  addCircleMarkers(data = listings_geo,
                   label = ~name)

m2 %>%
  addMarkers(data = listings_geo,
                   label = ~name)

Circle markers in leaflet.

Regular markers in leaflet.

markerClusterOptions

markerClusterOptions() can be added
- Shows aggregated values

Markers with cluster options.

m2 %>%
  addMarkers(data = listings_geo,

          clusterOptions = markerClusterOptions())

User selection

Add a addLayersControl() layer to allow users inputs
baseGroups: Allow users to toggle between different map providers
- Need to label each provider tile
- Set baseGroups as a vector containing these labels
overlayGroups: Allows users to toggle layers on and off
- Need to label each layer
- Set overlayGroups as a vector containing these labels

m_london <- leaflet(london_poly) %>% 

  addTiles(group="Default") %>% 
  addProviderTiles(providers$Stamen.Toner, 

                 group = "Toner") %>%

  addProviderTiles(providers$Esri.NatGeoWorldMap,

                 group = "Nat Geo") %>%

  addPolygons(col="red", label=~Name, 

                 group = "Ward") %>%

  addPolylines(loop_geo[,1], loop_geo[,2],

               group = "London loop") %>%

  addPolylines(capital_geo[,1], capital_geo[,2],
               labelOptions = labelOptions(noHide = TRUE),
               color = "orange", 

               group = "Capital ring", ) %>%

  addMarkers(data = listings_geo,
             clusterOptions = markerClusterOptions(),

             group = "Listings") %>%

  addLayersControl(

                      baseGroups = c("Default", "Toner", "Nat Geo"),

                    overlayGroups = c("Ward","Listings", 
                                       "London loop", "Capital loop"))

User selection, rendered

Leaflet map with user selection.

Let's practice!

Building Dashboards with shinydashboard