Mapping Your Data: Adding Markers and Routes with LeafletProxy in Shiny
Imagine you're building a Shiny application that lets users explore geographically-based data. You'd want to display points on a map, maybe even connect them with routes. This is where LeafletProxy comes in, a powerful tool within the Leaflet package for dynamic map manipulation in R.
The Problem:
You want to use Leaflet in your Shiny app to dynamically add markers and routes based on user input, without having to redraw the entire map each time.
Scenario:
Let's say you have a dataset of restaurants with their addresses. You want to display these restaurants on a map, allowing users to click on them to see their details. Additionally, you'd like to enable route visualization between selected restaurants.
Original Code (Simplified):
library(shiny)
library(leaflet)
# Sample restaurant data
restaurants <- data.frame(
name = c("Restaurant A", "Restaurant B", "Restaurant C"),
address = c("123 Main St, Anytown, USA", "456 Oak Ave, Anytown, USA", "789 Pine Rd, Anytown, USA")
)
# Shiny app UI
ui <- fluidPage(
leafletOutput("map"),
dataTableOutput("table")
)
# Shiny app server
server <- function(input, output, session) {
output$map <- renderLeaflet({
leaflet() %>%
setView(lng = -96.7970, lat = 32.7767, zoom = 5)
})
# Add markers on map click
observeEvent(input$map_click, {
leafletProxy("map") %>%
addMarkers(lng = input$map_click$lng, lat = input$map_click$lat)
})
output$table <- renderDataTable({
restaurants
})
}
shinyApp(ui, server)
Analysis and Clarification:
- LeafletProxy: This object allows you to interact with an existing Leaflet map without re-rendering it entirely.
- geocode(): We'll use this function from the 'ggmap' package to get coordinates from addresses.
- Dynamic Marker Addition: We'll capture user clicks on the map to add markers at those locations.
- Route Visualization: We'll use the 'leaflet.extras' package to draw routes between selected markers.
Enhanced Code:
library(shiny)
library(leaflet)
library(ggmap)
library(leaflet.extras)
# Sample restaurant data
restaurants <- data.frame(
name = c("Restaurant A", "Restaurant B", "Restaurant C"),
address = c("123 Main St, Anytown, USA", "456 Oak Ave, Anytown, USA", "789 Pine Rd, Anytown, USA")
)
# Get coordinates for restaurants
restaurants <- restaurants %>%
rowwise() %>%
mutate(lat = geocode(address)$lat,
lon = geocode(address)$lon)
# Shiny app UI
ui <- fluidPage(
leafletOutput("map"),
dataTableOutput("table")
)
# Shiny app server
server <- function(input, output, session) {
output$map <- renderLeaflet({
leaflet() %>%
setView(lng = -96.7970, lat = 32.7767, zoom = 5)
})
# Add markers for restaurants
observeEvent(input$map_click, {
leafletProxy("map") %>%
addMarkers(data = restaurants,
lng = ~lon, lat = ~lat,
popup = ~name)
})
# Add routes between clicked markers (using 'leaflet.extras')
observeEvent(input$map_click, {
leafletProxy("map") %>%
addPolylines(lng = c(input$map_click$lng, restaurants$lon[1]),
lat = c(input$map_click$lat, restaurants$lat[1]),
color = "blue", weight = 2)
})
output$table <- renderDataTable({
restaurants
})
}
shinyApp(ui, server)
Key Improvements:
- Geocoding: We use 'geocode()' to get coordinates for restaurant addresses.
- Dynamic Markers: Markers are added for each restaurant, and their popups display the restaurant name.
- Route Drawing: We use 'addPolylines' to dynamically draw routes between clicked points and a pre-selected restaurant (you can modify this to connect any two points).
- User Interaction: This setup allows users to explore the map and view routes between locations.
Further Considerations:
- User Selection: Implement user selection of restaurants to display routes between their chosen locations.
- Map Styling: Customize the map with features like basemaps, markers, and popups.
- Data Visualization: Integrate other data visualization methods (e.g., heatmaps, choropleths) to enrich your application.
Resources:
- Leaflet Package Documentation: https://rstudio.github.com/leaflet/
- ggmap Package Documentation: https://cran.r-project.org/web/packages/ggmap/index.html
- leaflet.extras Package Documentation: https://cran.r-project.org/web/packages/leaflet.extras/index.html
Conclusion:
With LeafletProxy and the power of R's mapping libraries, you can create interactive, dynamic map-based Shiny applications. This technique enables users to explore data geographically, visualize routes, and gain valuable insights from their interactions.
