Search code examples
rr-sftmapmultipolygonsosmdata

Impossible to plot OSM multipolygons in tmap and leaflet

I'm extracting data from OpenStreetMap using osmdata, and from the query I get a set of points, lines, polygons, and multipolygons. Somehow, when trying to plot multipolygons, leaflet and tmap do not find them, while using plot(st_geometry(...)) works well.

Any ideas as to what is happening?

library(osmdata)
library(sf)
library(tmap)

nkpg_schools <- 
  opq(bbox = "Norrköping") %>% 
  add_osm_feature(key = "amenity", value = "school") %>%
  osmdata_sf()

plot(st_geometry(nkpg_schools$osm_multipolygons)) #Works well

tmap_mode("view")
tm_basemap("Esri.WorldGrayCanvas") +
  tm_shape(nkpg_schools$osm_multipolygons) +
  tm_polygons()
#Does not work
Solution

  • This is an interesting problem! My first hunch was that the Norrköping schools multipolygon object was spatially invalid (which does happen with the OSM objects from time to time, unfortunately).

    This seems not to be the case, see sf::st_is_valid() test results.

    But! curiouser and curiouser: creating an intermediary object of schools made valid via sf::st_make_valid() causes the schools to behave themselves.

    I confess I can not fully explain what's going there, but if it solves your problem - who are we to judge?

    library(osmdata)
library(sf)
library(tmap)

nkpg_schools <- 
  opq(bbox = "Norrköping") %>% 
  add_osm_feature(key = "amenity", value = "school") %>%
  osmdata_sf()

st_is_valid(nkpg_schools$osm_multipolygons)
#[1] TRUE TRUE TRUE TRUE 

intmd <- nkpg_schools$osm_multipolygons %>% 
  st_make_valid()

tmap_mode("view")
tm_shape(intmd) +
  tm_polygons(col = "red") +
  tm_basemap("Esri.WorldGrayCanvas")

    Norrköping schools