Figuring out coordinates of a line in a shapefile

Question

I am working with a shapefile in R that is made up of 48 polygons. It is a map of Sweden with a line plotted to denote a biological boundary between north and south. I want to figure out the latitude of the line (see plot) but I cannot figure out how to extract that information from the shapefile.

I am wondering how to go about this. Can I plot each polygon separately to see if one/multiple polygons make up this line?

Answer 1

With the sf package you can very easily iterate over the geometries:

gadm <- raster::getData("GADM", country="SWE", level=1)

library("sf")
sf_geom <- st_geometry(st_as_sf(gadm))
# use st_read instead of st_as_sf to read the shapefile

for(i in seq_along(sf_geom)) {
  plot(sf_geom[i], main=i, axes=TRUE)
  Sys.sleep(1)
}