Here’s a very simple map

Just the basics

library(leaflet)

m <- leaflet() %>%
  addTiles() %>%  # Add default OpenStreetMap map tiles
  addMarkers(lng=3.7174, lat=51.0543, popup="I'm somewhere around here") %>%
   setView(lng=3.7174, lat=51.0543, zoom = 12)
m  # Print the map

A more difficult one

I spent the whole time working on this code and encountered this problem

Anyhow, if you know how to fix this, please send me a mail @ geowizard at gmail.com Here is the code :

# Download data from https://data.stad.gent/datasets/wijken 
Vlaanderen <- readOGR("StatSect/Shapefile/statsec.shp", "statsec")
Gent <- Vlaanderen[Vlaanderen@data$NISCODE == 44021,]
# to see type plot(Gent)

Gentpro <- spTransform(Gent, CRS("+proj=longlat +ellps=intl"))

BuiltArea <- read.csv("bebouwdeoppervlakte2.csv", encoding="latin1", sep=";", dec=".")

ChronicDis <- read.csv("chronischeaandoeningen2.csv", encoding="latin1", sep=";", dec=".")



palette <- colorBin(c('#f7fbff', '#deebf7', '#c6dbef', '#9ecae1', '#6baed6', '#4292c6', '#2171b5', '#08519c', '#08306b'), 
                    bins = c(0, 5, 10, 15, 20, 25, 30, 40, 50, 60))


popup1 <- paste0("Built Area %","<br>District: ",             
                      Gentpro$SECNAAM,         #column containing the district names
                      "<br>Percentage: ", 
                      BuiltArea$bebouwingsgraad_pct          #column that contains the relative amount data
                      ,"<br>Total km²: ", 
                      BuiltArea$oppervlakte_km2           #column that contains the absolute amount data
)

 
popup2 <- paste0("Chronic Disease %",
                      "<br>District: ",             
                      Gentpro$SECNAAM,         #column containing the district names
                      "<br>Percentage: ", 
                      ChronicDis$Percentage_personen_met_chronische_aandoeningen          #column that contains the relative amount data
                      ,"<br>Total : ", 
                      ChronicDis$Aantal_personen_met_chronische_aandoeningen           #column that contains the absolute amount data
)




mymap <- leaflet() %>% 
addProviderTiles("Hydda.Full", options = tileOptions(minZoom=9, maxZoom=14)) %>% #"freeze" the mapwindow to max and min zoomlevel

addPolygons(data = Gentpro, 
            fillColor = ~palette(BuiltArea$bebouwingsgraad_pct),  
            fillOpacity = 0.6,         ## how transparent do you want the polygon to be?
            color = "white",       ## color of borders between districts
            weight = 1.5,            ## width of borders
            popup = popup1,         ## which popup?
            group="Built Area %")%>%  
              

## for the second layer we mix things up a little bit, so you'll see the difference in the map!
addPolygons(data = Gentpro, 
            fillColor = ~palette(ChronicDis$Percentage_personen_met_chronische_aandoeningen), 
            fillOpacity = 0.2, 
            color = "white", 
            weight = 1.5, 
            popup = popup2, 
            group="Chronic Disease %")%>%

addLayersControl(
    baseGroups = c("Built Area %", ## group 1
                   "Chronic Disease %" ## group 2
    ),
    options = layersControlOptions(collapsed = FALSE))%>% ## we want our control to be seen right away

addLegend(position = 'topleft', ## choose bottomleft, bottomright, topleft or topright
           colors = c('#f7fbff', '#deebf7', '#c6dbef', '#9ecae1', '#6baed6', '#4292c6', '#2171b5', '#08519c', '#08306b'),
           labels = c('0','5','10','15','20','25','30','40','60'),  ## legend labels (only min and max)
           opacity = 0.6,      ##transparency again
           title = "%")   ## title of the legend

mymap