Shapefile issues in leaflet in R: Boundaries not showing for choropleth map

General
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1

I am trying to make a choropleth map with imported shapefiles of districts.

I think my data is aligned with map because one district I was expecting lit up(but I am not sure). The problem is that I cannot see the shp file boundaries.

I used the code below:

districtsg <-readOGR("sample/copyfile/Districts/Map_of_Districts_.shp")

districtsg <- sp::spTransform(districtsg, CRS("+proj=longlat +datum=WGS84"))

districtsg <-subset(districtsg,is.element(districtsg$NAME,fb$districtlive))

fb <- fb [order(match(fb$districtlive,districtsg$NAME)),]



bins <- c(0,10,20,30,40,50)
pal<-colorBin("YlOrRd",domain=fb$per.content, bins=bins)


m<- leaflet() %>%
   setView(lng = -1.0232,lat=7.9465,zoom = 6) %>%
   addProviderTiles(providers$Stamen.Toner)%>%
   addPolygons(data =districtsg,
               weight = 1,
               smoothFactor = 0.5,
               color = "Blue",
               fillOpacity = 0.8,
               fillColor= ~pal(fb$per.content),
               highlight=highlightOptions(
                  weight = 5,
                  color = "#666666",
                  dashArray = "",
                  fillOpacity = 0.7,
                  bringToFront = TRUE
               ))
m

labels <- paste(  "<p>", fb$districtlive,"</p>",
                  "<p>", "% content:",round(fb$per.content,digits = 3),"</p>",
                  "<p>", "Total people that content:",round(fb$totalcontent,digits = 3),"</p>",
                  "<p>", "Total respondents from this district:",round(fb$totalrespondents,digits = 3),"</p>",sep = "" )



m<- leaflet() %>%
   setView(lng = -1.0232,lat=7.9465,zoom = 6) %>%
   addProviderTiles(providers$Stamen.Toner)%>%
   addPolygons(data =districtsg,
               weight = 1,
               smoothFactor = 0.5,
               color = "Blue",
               fillOpacity = 0.8,
               fillColor= ~pal(fb$per.content),
               highlight=highlightOptions(
                  weight = 5,
                  color = "#666666",
                  dashArray = "",
                  fillOpacity = 0.7,
                  bringToFront = TRUE
               ),
               label = lapply(labels,HTML)) %>%

     addLegend("topright",pal=pal, values = fb$per.content,
             opacity = 0.7,
              )
m

I looked around and found that the code below worked for someone, i tried it but it didn't work for me.

PRO <- sp::CRS('+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0')
DAT <- sp::spTransform(districtsg,PRO)

I am trying to make a choropleth map where districts boundaries can be seen and interacted with.

I used a sample data to do this and only one district was above 0. That district was the only that was coloured. I was expecting the other districts boundaries lines to present(and interactive) even if it had a 0% content and it was not coloured.

I did not get any error while doing this, it is just that, my map did look like what i was expecting.

I'd appreciate input on how to have my shape files on top of the tiles, with my data values present on top.

2

I suspect the issue is with this line

 districtsg <-subset(districtsg,is.element(districtsg$NAME,fb$districtlive))

You are subsetting your districts according to a condition that is not obvious from your code.

Try removing this line, and see what happens.

You might also consider moving from {rgdal} / {sp} based workflow to {sf} workflow = read the data in via districtsg <-sf::st_read("sample/copyfile/Districts/Map_of_Districts_.shp").

{sf} objects are modified data frames, and in general easier to troubleshoot than sui generis {sp} objects.

3

I tried what you suggested using this code:

districtsg <-sf::st_read("sample/copyfile/Districts/Map_of_Districts_.shp")
districtsg <- sp::spTransform(districtsgh, CRS("+proj=longlat +datum=WGS84"))

and I got this error

Error in (function (classes, fdef, mtable)  : 
  unable to find an inherited method for function ‘spTransform’ for signature ‘"sf", "CRS"’

I removed the sf-transform code:

districtsg <- sp::spTransform(districtsgh, CRS("+proj=longlat +datum=WGS84"))

and run it and ended up with this warning:

Warning messages:
1: In pal(fb$per.content) :
  Some values were outside the color scale and will be treated as NA
2: sf layer is not long-lat data

Do you help me understand why the first error messaged happend?

4

The spTransform line can be functionally replaced by districtsg <- sf::st_transform(districtsgh, 4326).

What this line does (and the previous in {sp} environment did) is that it transforms the coordinate reference system of your object from the current (unknown to us) to WGS84 which is in latitude & longitude and understood by leaflet.

The warning about palettes is not relevant to your problem of not showing borders, as it applies to fill of your polygons.