Leaflet with multiple polylines elements leads to huge HTML - r

Question

I'm building a leaflet map on R having multiple layers that are controlled by addLayersControl. Every layer as the same spatial information, so only the data associated to each polylines changes. The idea is to have a basic map, where the user decide which data field is display. I succeeded at making the map, however I noticed that the size of the html file produced is huge.
In my actual context, making the map with only one layer leads to a ~20mb file. However, if I add one field it gets to ~40mb and three layer ~60mb. So it seems to me that the html produced is loading the same shapefile 3 times instead of simply using one shapefile and linking it a data frame of some sort.
Am I stock with this behavior of leaflet or is there a way to file size inflation in my context? I may not have programmed my leaflet the better way...
I've made a reproducible example to show the problem. It uses a small shapefile so the size problem is not dramatic, however the point is the same, which is constantly doubling file size. Also, the example is lengthy, sorry about that, I could'n find a way to simplify it further.
Preparation:
# loading the libraries
library(sf)
library(leaflet)
library(htmlwidgets)
# preparing the shapefile
nc <- st_read(system.file("gpkg/nc.gpkg", package="sf"), quiet = TRUE) %>%
st_transform(st_crs(4326))
# preparing the colors (not really important)
pal.area <- colorNumeric(palette = "inferno", domain = range(nc$AREA))
pal.perim <- colorNumeric(palette = "inferno", domain = range(nc$PERIMETER))
pal.cnty <- colorNumeric(palette = "inferno", domain = range(nc$CNTY_))
pal.sid74 <- colorNumeric(palette = "inferno", domain = range(nc$SID74))
Making the leaflet, this section is long, however it's simply 4 leaflet maps created one after another by adding one layer at a time. It's mostly copy-pasted work:
###
one_layer <- leaflet(data = nc) %>%
addTiles() %>%
addPolylines(fillColor = ~pal.area(AREA),
fill = TRUE,
opacity = 0.8,
group = "area") %>%
addLegend("bottomright",
pal = pal.area, values = ~AREA,
opacity = 1, group = "area"
)
###
###
two_layers <- leaflet(data = nc) %>%
addTiles() %>%
addPolylines(fillColor = ~pal.area(AREA),
fill = TRUE,
opacity = 0.8,
group = "area") %>%
addLegend("bottomright",
pal = pal.area, values = ~AREA,
opacity = 1, group = "area") %>%
addPolylines(fillColor = ~pal.perim(PERIMETER),
fill = TRUE,
opacity = 0.8,
group = "perim") %>%
addLegend("bottomright",
pal = pal.perim, values = ~PERIMETER,
opacity = 1, group = "perim"
) %>%
addLayersControl(
overlayGroups = c("area", "perim"), position = "bottomleft",
options = layersControlOptions(collapsed = FALSE)
)
###
###
three_layers <- leaflet(data = nc) %>%
addTiles() %>%
addPolylines(fillColor = ~pal.area(AREA),
fill = TRUE,
opacity = 0.8,
group = "area") %>%
addLegend("bottomright",
pal = pal.area, values = ~AREA,
opacity = 1, group = "area") %>%
addPolylines(fillColor = ~pal.perim(PERIMETER),
fill = TRUE,
opacity = 0.8,
group = "perim") %>%
addLegend("bottomright",
pal = pal.perim, values = ~PERIMETER,
opacity = 1, group = "perim"
) %>%
addPolylines(fillColor = ~pal.cnty(CNTY_),
fill = TRUE,
opacity = 0.8,
group = "cnty") %>%
addLegend("bottomright",
pal = pal.cnty, values = ~CNTY_,
opacity = 1, group = "cnty"
) %>%
addLayersControl(
overlayGroups = c("area", "perim", "cnty"), position = "bottomleft",
options = layersControlOptions(collapsed = FALSE)
) %>%
hideGroup(c("perim","cnty"))
###
###
four_layers <- leaflet(data = nc) %>%
addTiles() %>%
addPolylines(fillColor = ~pal.area(AREA),
fill = TRUE,
opacity = 0.8,
group = "area") %>%
addLegend("bottomright",
pal = pal.area, values = ~AREA,
opacity = 1, group = "area") %>%
addPolylines(fillColor = ~pal.perim(PERIMETER),
fill = TRUE,
opacity = 0.8,
group = "perim") %>%
addLegend("bottomright",
pal = pal.perim, values = ~PERIMETER,
opacity = 1, group = "perim"
) %>%
addPolylines(fillColor = ~pal.cnty(CNTY_),
fill = TRUE,
opacity = 0.8,
group = "cnty") %>%
addLegend("bottomright",
pal = pal.cnty, values = ~CNTY_,
opacity = 1, group = "cnty"
) %>%
addPolylines(fillColor = ~pal.sid74(SID74),
fill = TRUE,
opacity = 0.8,
group = "sid74") %>%
addLegend("bottomright",
pal = pal.sid74, values = ~SID74,
opacity = 1, group = "sid74"
) %>%
addLayersControl(
overlayGroups = c("area", "perim", "cnty", "sid74"), position = "bottomleft",
options = layersControlOptions(collapsed = FALSE)
) %>%
hideGroup(c("perim","cnty", "sid74"))
###
Then, you get 4 objects (maps) we can compare their size directly in R:
object.size(one_layer)
301864 bytes
object.size(two_layers)
531144 bytes
object.size(three_layers)
681872 bytes
object.size(four_layers)
828616 bytes
The size increase is constant and way higher that what we would expect if the only the data was added instead of all the spatial info. As a comparison, the initial shape which has 15 fields is of size:
object.size(nc)
135360 bytes
If we save the maps to HTML, the problem is even more visible:
saveWidget(one_layer, paste0(getwd(),"/temp_data/temp/one_layer.html"), selfcontained = F)
saveWidget(two_layers, paste0(getwd(),"/temp_data/temp/two_layers.html"), selfcontained = F)
saveWidget(three_layers, paste0(getwd(),"/temp_data/temp/three_layers.html"), selfcontained = F)
saveWidget(four_layers, paste0(getwd(),"/temp_data/temp/four_layers.html"), selfcontained = F)
file.info(list.files("temp_data/temp", pattern = ".html$", full.names = T))$size[c(2,4,3,1)] %>%
setNames(c("One Layer", "Two Layers", "Three Layers", "Four Layers")) %>%
barplot(ylab="size in Bytes")
It's clearly doubling in size.
So, to summarize, is there a way to get leaflet to not reproduced the spatial information when adding multiple fields of data to the same map?