I have one sf object with US counties, and another with US congressional districts. I need to know (i) which counties are in which congressional district, and (ii) if one county overlaps the district boundary (i.e. is contained within two districts) then I need to know which district it's in "more", or what proportion of the county lays in each.
Here are my exact sf objects:
library(USAboundaries)
library(sf)
union_states <- c("Maine", "New Hampshire", "Vermont", "New York", "Massachusetts", "Rhode Island", "Connecticut", "Pennsylvania", "New Jersey", "Ohio", "Indiana", "Illinois", "Iowa", "Wisconsin", "Minnesota", "Michigan") # only core states: exluces CA, WA, KS, and boundary states
union_sf <- us_counties(map_date = "1865-01-01", states = union_states, resolution = 'high')
union_congress_sf <- us_congressional(resolution = "low", states = union_states)
This question poses my exact question, but is a bit outdated and doesn't work with sf objects: Using R intersections to create a polygons-inside-a-polygon key using two shapefile layers
You can use st_join() with the largest = TRUE argument.
For the counties and congressional districts objects, I removed most of the columns so the result is cleaner. In the output, name is the county, and geoid is the congressional district.
library(dplyr)
union_sf <- union_sf %>%
select(name, geometry)
union_congress_sf <- union_congress_sf %>%
select(geoid, state_name, geometry)
join <- st_join(union_sf,
union_congress_sf,
largest = TRUE)
join
Simple feature collection with 804 features and 3 fields
geometry type: MULTIPOLYGON
dimension: XY
bbox: xmin: -97.23421 ymin: 36.97353 xmax: -66.94993 ymax: 49.38437
geographic CRS: WGS 84
First 10 features:
name geoid state_name geometry
2455 FAIRFIELD 0904 Connecticut MULTIPOLYGON (((-73.5055 41...
2481 HARTFORD 0901 Connecticut MULTIPOLYGON (((-72.81354 4...
2495 LITCHFIELD 0905 Connecticut MULTIPOLYGON (((-73.00875 4...
2497 MIDDLESEX 0902 Connecticut MULTIPOLYGON (((-72.52454 4...
2541 NEW HAVEN 0903 Connecticut MULTIPOLYGON (((-72.93861 4...
2554 NEW LONDON 0902 Connecticut MULTIPOLYGON (((-72.33685 4...
2560 TOLLAND 0902 Connecticut MULTIPOLYGON (((-72.10217 4...
2569 WINDHAM 0902 Connecticut MULTIPOLYGON (((-71.79924 4...
4443 ADAIR 1903 Iowa MULTIPOLYGON (((-94.24152 4...
4444 ADAMS 1903 Iowa MULTIPOLYGON (((-94.47062 4...