stat_sf_coordinates()
extracts the coordinates from 'sf' objects and
summarises them to one pair of coordinates (x and y) per geometry. This is
convenient when you draw an sf object as geoms like text and labels (so
geom_sf_text()
and geom_sf_label()
relies on this).
stat_sf_coordinates(mapping = aes(), data = NULL, geom = "point", position = "identity", na.rm = FALSE, show.legend = NA, inherit.aes = TRUE, fun.geometry = NULL, ...)
mapping  Set of aesthetic mappings created by 

data  The data to be displayed in this layer. There are three options: If A A 
geom  The geometric object to use display the data 
position  Position adjustment, either as a string, or the result of a call to a position adjustment function. 
na.rm  If 
show.legend  logical. Should this layer be included in the legends?

inherit.aes  If 
fun.geometry  A function that takes a 
...  Other arguments passed on to 
coordinates of an sf
object can be retrieved by sf::st_coordinates()
.
But, we cannot simply use sf::st_coordinates()
because, whereas text and
labels require exactly one coordinate per geometry, it returns multiple ones
for a polygon or a line. Thus, these two steps are needed:
Choose one point per geometry by some function like sf::st_centroid()
or sf::st_point_on_surface()
.
Retrieve coordinates from the points by sf::st_coordinates()
.
For the first step, you can use an arbitrary function via fun.geometry
.
By default, function(x) sf::st_point_on_surface(sf::st_zm(x))
is used;
sf::st_point_on_surface()
seems more appropriate than sf::st_centroid()
since lables and text usually are intended to be put within the polygon or
the line. sf::st_zm()
is needed to drop Z and M dimension beforehand,
otherwise sf::st_point_on_surface()
may fail when the geometries have M
dimension.
X dimension of the simple feature
Y dimension of the simple feature
if (requireNamespace("sf", quietly = TRUE)) { nc < sf::st_read(system.file("shape/nc.shp", package="sf")) ggplot(nc) + stat_sf_coordinates() ggplot(nc) + geom_errorbarh( aes(geometry = geometry, xmin = stat(x)  0.1, xmax = stat(x) + 0.1, y = stat(y), height = 0.04), stat = "sf_coordinates" ) }#> Reading layer `nc' from data source `/home/travis/R/Library/sf/shape/nc.shp' using driver `ESRI Shapefile' #> Simple feature collection with 100 features and 14 fields #> geometry type: MULTIPOLYGON #> dimension: XY #> bbox: xmin: 84.32385 ymin: 33.88199 xmax: 75.45698 ymax: 36.58965 #> epsg (SRID): 4267 #> proj4string: +proj=longlat +datum=NAD27 +no_defs#> Warning: st_point_on_surface may not give correct results for longitude/latitude data