This is more of a general question regarding R Leaflet than a specific coding problem. Google hasn't been too helpful for me this morning so I'm reaching out to the SO community in the hope that someone can help.
I know that it is possible to include tiled WMS data into a leaflet map using addWMSTiles(). This is useful if the aim is to understand the spatial distribution of your data without reference to any information associated with that spatial data (e.g. the area that a rendered shape takes up, or the name of that shape etc.). To resolve this, it's possible to specify a shapefile polygon instead using addPolygons(). This allows Leaflet to display data associated with each polygon using a click/mouse over (e.g. mousing over a polygon could tell you the name of that feature, it's area and even a hyperlink to external data).
The problem with shapefiles is that they're computationally expensive to render when the area of extent becomes large, even if the polygons are simplified (e.g. using st_simplify() or similar process). In addition, if your mapping application has several shapefile layers, the render time increases as some function of the number of layers and it can quickly get out of hand.
I am therefore wondering if there is a way to render polygons on-screen in a similar way to rendering tiles? That is, the polygons are only rendered when the user is focussed on a particular area. This way, you have all of the benefits of polygons and associated data but with the substantially faster rendering times of tiled datasets.
I stumbled across WFS in R during my research (e.g. here) which I initially thought would be my saviour, but in the few examples I've come across, it seems that it's necessary to first download all the spatial data (e.g. using st_read()) before plotting it on a map, which doesn't seem to address the loading/rendering time issue that I have detailed previously.
As there is no addWFSTiles() function within leaflet(), I suspect it's not possible to have my cake and eat it too. However, if there is some reasonably robust 'hacky' way to solve the rendering time issue, I am certainly all-ears. For context, my ultimate aim is to present my maps within an R Shiny application so fast rendering times and reduced bandwidth requirements via tiling would be an optimal solution for me. I'm not sure whether caching could be a viable solution so would be keen to discuss this aspect further if someone thinks it might be useful.
Based on the comments associated with this question, I have copied some basic code below which displays the distribution of ancient woodland in England. It uses WMS data provided by Natural England (source here.)
library(leaflet)
library(leaflet.extras)
leaflet() %>%
setView(zoom=11, lng=-1.19, lat=52.8) %>%
# Defines open-source base maps
addProviderTiles(group = "OpenSM", providers$OpenStreetMap) %>%
# Defines ancient woodland WMS from Natural England
addWMSTiles(group = "Ancient Woodland",
baseUrl = "https://environment.data.gov.uk/spatialdata/ancient-woodland-england/wms?",
layers = "Ancient_Woodland_England",
options = WMSTileOptions(format = "image/png", transparent = TRUE, crs = "EPSG:4326", interactive = TRUE, minZoom = 7, maxZoom = 15)) %>%
addLayersControl(
baseGroups = c("OpenSM"),
overlayGroups = c("Ancient Woodland"),
options = layersControlOptions(collapsed = FALSE)
)
For now, it would be interesting to see whether this data can be 'interactive' in the sense that upon clicking a patch of woodland, its name/area etc. can be displayed as a popup. If WMS is able to do this, I can test adding 10-20 different layers to assess performance across the UK. However, as I mentioned in the original iteration of this question, I don't think it's possible to have this functionality in WMS (but could potentially be viable with WFS).
