How to access polygon information from shapefile leaflet R

Question

I made a map of London using https://data.london.gov.uk/dataset/statistical-gis-boundary-files-london and shiny and R and leaflet. I added an attribute to the shapefile, and now want to be able to highlight the shapefile and print information when the user clicks on a specific polygon.

I looked at shiny leaflet ploygon click event, Marker mouse click event in R leaflet for shiny, and How to implement input$map_marker_click correctly?, and know I need to use ObserveEvent, but have not been able to implement it correctly.

My code is:

library(shiny)
library("rgdal")
library(leaflet)

shapeData <- readOGR('statistical-gis-boundaries-london/ESRI/LSOA_2004_London_Low_Resolution.shp')
shapeData <- spTransform(shapeData, CRS("+proj=longlat +ellps=GRS80"))
shapeData$col=sample(c('red','yellow','green'),nrow(shapeData),1) #add some value you want to map
borough=read.csv('BoroughCentres.csv')

ui=fluidPage(
  fluidPage(
    leafletOutput('LSOAMap'),
    p(),
    selectInput('LANAME','Borough',
                choices = unique(shapeData$LA_NAME))
  )

) 


server=function(input, output) {

  output$LSOAMap <- renderLeaflet({
    llong=borough[borough$Borough==input$LANAME,3]
    llat=borough[borough$Borough==input$LANAME,4]

   bor=subset(shapeData,shapeData$LA_NAME %in% input$LANAME)
    leaflet()  %>% addTiles() %>% 
      setView(lng = llong, lat=llat,zoom=13) %>% 
      addPolygons(data=bor,weight=2,col = 'black',fillOpacity = 0.2,fillColor = bor$col,
                  highlightOptions = highlightOptions(color='white',weight=1,
                                                      bringToFront = TRUE)) %>% 
      addMarkers(lng = llong,lat=llat,popup=input$LANAME) 
  }) 

}
shinyApp(ui, server)

I tried adding, along with session as an argument:

  observe({
    click <- input$map_marker_click
    if (is.null(click))
      return()

    print(click)
    text <-
      paste("Lattitude ",
            click$lat,
            "Longtitude ",
            click$lng)

    leafletProxy(mapId = "LSOAMap") %>%
      clearPopups() %>%
      addPopups(dat = click, lat = ~lat, lng = ~lng, popup = text)

    # map$clearPopups()
    # map$showPopup(click$latitude, click$longtitude, text)
  })

to no avail.

What I want is that when a user highlights a specific shape, text pops up and shows the corresponding STWARDNAME from the shapefile.

the first few lines of borough are:

> head(borough)
               Borough   LA_CODE        long      lat
1       City of London E09000001 -0.09194991 51.51814
2 Barking and Dagenham E09000002  0.13064556 51.54764
3               Barnet E09000003 -0.20416711 51.61086
4               Bexley E09000004  0.13459320 51.45981
5                Brent E09000005 -0.26187070 51.55697
6              Bromley E09000006  0.03734663 51.38836

csv file is simple df of central points of the borough. How can I share it? — frank, Aug 29 '18 at 13:06

score 2 · Accepted Answer · answered Aug 30 '18 at 08:17

You are pretty close but have a few syntax issues which I think are tripping you up.

First you are not properly selecting what STWARDNAME you want from your SPDF so there is no way for R to know which one to show. I added this line

popup = subset(shapeData, LA_NAME == input$LANAME )$STWARDNAME

Also you were passing highlightOptions as an option when it should just be highlight

Finally since you were more interested in mouseover for a polygon, I removed the popup marker and changed to highlight so that the name is shown when you mouseover the polygon:

leaflet()  %>% addTiles() %>% 
  setView(lng = llong, lat=llat,zoom=13) %>% 
  addPolygons(data=bor,weight=2,col = 'black',fillOpacity = 0.2,fillColor = bor$col,
              highlight = highlightOptions(color='white',weight=1,
                                                  bringToFront = TRUE), label= popup)

Which yields:

score 0 · Answer 2 · answered Aug 30 '18 at 11:42

@Stedy answer was brilliant, and better, I just went a different way. I added in a layer id vector, and a popup decision to find the STWARDNAME

lid=as.vector(row.names(bor@data))
pu=bor@data[row.names(bor@data)==lid,'STWARDNAME']

, then added in two arguments while making the map layerId = lid,popup = pu,. The pop up showed when the user clicked on an area

bor=subset(shapeData,shapeData$LA_NAME %in% input$LANAME)
lid=as.vector(row.names(bor@data))
pu=bor@data[row.names(bor@data)==lid,'STWARDNAME']
leaflet()  %>% addTiles() %>% 
  setView(lng = llong, lat=llat,zoom=13) %>% 
  addPolygons(data=bor,weight=2,col = 'black',fillOpacity = 0.2,fillColor = bor$col,
              layerId = lid,popup = pu,
              highlightOptions = highlightOptions(color='white',weight=1,
                                                  bringToFront = TRUE)) %>% 
  addMarkers(lng = llong,lat=llat,popup=input$LANAME)

How to access polygon information from shapefile leaflet R

2 Answers2

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