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).
Usage
stat_sf_coordinates(
mapping = aes(),
data = NULL,
geom = "point",
position = "identity",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE,
fun.geometry = NULL,
...
)
Arguments
- mapping
Set of aesthetic mappings created by
aes()
. If specified andinherit.aes = TRUE
(the default), it is combined with the default mapping at the top level of the plot. You must supplymapping
if there is no plot mapping.- data
The data to be displayed in this layer. There are three options:
If
NULL
, the default, the data is inherited from the plot data as specified in the call toggplot()
.A
data.frame
, or other object, will override the plot data. All objects will be fortified to produce a data frame. Seefortify()
for which variables will be created.A
function
will be called with a single argument, the plot data. The return value must be adata.frame
, and will be used as the layer data. Afunction
can be created from aformula
(e.g.~ head(.x, 10)
).- geom
The geometric object to use to display the data, either as a
ggproto
Geom
subclass or as a string naming the geom stripped of thegeom_
prefix (e.g."point"
rather than"geom_point"
)- position
Position adjustment, either as a string naming the adjustment (e.g.
"jitter"
to useposition_jitter
), or the result of a call to a position adjustment function. Use the latter if you need to change the settings of the adjustment.- na.rm
If
FALSE
, the default, missing values are removed with a warning. IfTRUE
, missing values are silently removed.- show.legend
logical. Should this layer be included in the legends?
NA
, the default, includes if any aesthetics are mapped.FALSE
never includes, andTRUE
always includes. It can also be a named logical vector to finely select the aesthetics to display.- inherit.aes
If
FALSE
, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g.borders()
.- fun.geometry
A function that takes a
sfc
object and returns asfc_POINT
with the same length as the input. IfNULL
,function(x) sf::st_point_on_surface(sf::st_zm(x))
will be used. Note that the function may warn about the incorrectness of the result if the data is not projected, but you can ignore this except when you really care about the exact locations.- ...
Other arguments passed on to
layer()
. These are often aesthetics, used to set an aesthetic to a fixed value, likecolour = "red"
orsize = 3
. They may also be parameters to the paired geom/stat.
Details
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()
orsf::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.
Computed variables
These are calculated by the 'stat' part of layers and can be accessed with delayed evaluation.
after_stat(x)
X dimension of the simple feature.after_stat(y)
Y dimension of the simple feature.
Examples
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 = after_stat(x) - 0.1,
xmax = after_stat(x) + 0.1,
y = after_stat(y),
height = 0.04),
stat = "sf_coordinates"
)
}
#> Reading layer `nc' from data source
#> `/home/runner/work/_temp/Library/sf/shape/nc.shp' using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension: XY
#> Bounding box: xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS: NAD27
#> Warning: st_point_on_surface may not give correct results for longitude/latitude data