R SF – How to Create Multipolygon from Overlapping Polygons Using sf Package in R

Question

I'm trying to remove overlapping areas from multiple polygons using sf like the following:

# sample polygon
poly <- data.frame(
    lon = c(0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 2, 2, 0.8, 1, 1, 2, 2, 1, 1),
    lat = c(0, 0, 1, 1.5, 0, 1, 1, 2, 2, 1, 1, 1, 2, 2, 1, 0, 0, 1, 1, 0),
    var = c(1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3 ,3 ,3 ,3 ,3, 4 ,4 ,4, 4, 4)
  ) %>%
  st_as_sf(coords = c("lon", "lat"), dim = "XY") %>% st_set_crs(4326) %>% 
group_by(var) %>%
  summarise(geometry = st_union(geometry), do_union = F) %>% st_cast("POLYGON")

In my data there are several hundred polygons and many of them are overlapping multiple times. So it would be great if there is a way to remove overlapping areas from a sf dataframe like in the example. I tried something with st_difference but I thought there might be a better way than applying this to each pair of polygons which would result in too many permutations.

Answer 1

You can do the intersection of polygons and then filter those that overlap.

inter <- st_intersection(poly) %>% filter(n.overlaps < 2)
plot(inter %>% select(var)