I am making some maps in Leaflet in R, and the maps consist of a polygon layer as well as a layer of markers. The polygon usually covers a larger area than the markers, but I want to zoom specifically to the marker area.
I know I can manually specify lat/longs and zoom level, but I don't want to do that because this code will generate a lot of different maps covering different subsets of my dataset (or on different datasets).
Here's a simplified version of the code that generates the map. I don't think this necessarily requires a full reprex to answer the question but can do so if necessary.
addProviderTiles(providers$CartoDB.Positron, group = "Basemap") %>%
addPolygons(data = seat_boundary, fillColor = "white", fillOpacity = 0.0, weight = 1.5, opacity = 0.6, color = "red", group = "Seat boundary") %>%
addCircleMarkers(data = formalvotes_by_booth_subarea, fillColor = ~subarea_pal(sub_areas), lng=~longitude, lat=~latitude, radius = ~circle_size, fillOpacity = 1, color = 'white', opacity = 1, weight = 1.2, popup = ~popup) %>%
addLegend(pal = subarea_pal, values = formalvotes_by_booth_subarea$sub_areas, opacity = 1)```
I also think I might be able to half-solve this problem by averaging the max and min latitude and max and min longitude in the markers dataset to come up with a central point to focus the map on, but it wouldn't ensure the zoom would be correct (indeed I'm not sure if you can set the lat/long and not set the zoom).
Have you tried fitBounds?
Starting from what you have posted, I would first get the bbox coordinates of your markers:
library(sf)
bounds <- markers %>%
st_bbox() %>%
as.character()
Then passing them into the fitBounds function:
library(leaflet)
leaflet %>%
addPolygons(data = polygons) %>%
addCircleMarkers(data = markers) %>%
fitBounds(bounds[1], bounds[2], bounds[3], bounds[4])