ggsf
Visualise sf objects
This set of geom, stat, and coord are used to visualise simple feature (sf)
objects. For simple plots, you will only need geom_sf as it
uses stat_sf and adds coord_sf for you. geom_sf is
an unusual geom because it will draw different geometric objects depending
on what simple features are present in the data: you can get points, lines,
or polygons.
- Keywords
- datasets
Usage
stat_sf(mapping = NULL, data = NULL, geom = "rect",
position = "identity", na.rm = FALSE, show.legend = NA,
inherit.aes = TRUE, ...)geom_sf(mapping = aes(), data = NULL, stat = "sf",
position = "identity", na.rm = FALSE, show.legend = NA,
inherit.aes = TRUE, ...)
coord_sf(xlim = NULL, ylim = NULL, expand = TRUE, crs = NULL,
datum = sf::st_crs(4326), ndiscr = 100, default = FALSE)
Arguments
- mapping
Set of aesthetic mappings created by
aes()oraes_(). If specified andinherit.aes = TRUE(the default), it is combined with the default mapping at the top level of the plot. You must supplymappingif 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
functionwill be called with a single argument, the plot data. The return value must be adata.frame., and will be used as the layer data.- 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
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.FALSEnever includes, andTRUEalways includes.You can also set this to one of "polygon", "line", and "point" to override the default legend.
- 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().- ...
Other arguments passed on to
layer(). These are often aesthetics, used to set an aesthetic to a fixed value, likecolor = "red"orsize = 3. They may also be parameters to the paired geom/stat.- stat
The statistical transformation to use on the data for this layer, as a string.
- xlim
Limits for the x and y axes.
- ylim
Limits for the x and y axes.
- expand
If
TRUE, the default, adds a small expansion factor to the limits to ensure that data and axes don't overlap. IfFALSE, limits are taken exactly from the data orxlim/ylim.- crs
Use this to select a specific CRS. If not specified, will use the CRS defined in the first layer.
- datum
CRS that provides datum to use when generating graticules
- ndiscr
number of segments to use for discretizing graticule lines; try increasing this when graticules look unexpected
- default
Is this the default coordinate system? If
FALSE(the default), then replacing this coordinate system with another one creates a message alerting the user that the coordinate system is being replaced. IfTRUE, that warning is suppressed.
Geometry aesthetic
geom_sf uses a unique aesthetic: geometry, giving an
column of class sfc containg simple features data. There
are three ways to supply the geometry aesthetic:
Do nothing: by default
geom_sfassumes it is stored in thegeometrycolumn.Explicitly pass an
sfobject to thedataargument. This will use the primary geometry column, no matter what it's called.Supply your own using
aes(geometry = my_column)
Unlike other aesthetics, geometry will never be inherited from
the plot.
CRS
coord_sf() ensures that all layers use a common CRS. You can
either specify it using the CRS param, or coord_sf will
take it from the first layer that defines a CRS.
Examples
# NOT RUN {
if (requireNamespace("sf", quietly = TRUE)) {
nc <- sf::st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)
ggplot(nc) +
geom_sf(aes(fill = AREA))
# If not supplied, coord_sf() will take the CRS from the first layer
# and automatically transform all other layers to use that CRS. This
# ensures that all data will correctly line up
nc_3857 <- sf::st_transform(nc, "+init=epsg:3857")
ggplot() +
geom_sf(data = nc) +
geom_sf(data = nc_3857, colour = "red", fill = NA)
# Unfortunately if you plot other types of feature you'll need to use
# show.legend to tell ggplot2 what type of legend to use
nc_3857$mid <- sf::st_centroid(nc_3857$geometry)
ggplot(nc_3857) +
geom_sf(colour = "white") +
geom_sf(aes(geometry = mid, size = AREA), show.legend = "point")
# You can also use layers with x and y aesthetics: these are
# assumed to already be in the common CRS.
ggplot(nc) +
geom_sf() +
annotate("point", x = -80, y = 35, colour = "red", size = 4)
# Thanks to the power of sf, a geom_sf nicely handles varying projections
# setting the aspect ratio correctly.
library(maps)
world1 <- sf::st_as_sf(map('world', plot = FALSE, fill = TRUE))
ggplot() + geom_sf(data = world1)
world2 <- sf::st_transform(
world1,
"+proj=laea +y_0=0 +lon_0=155 +lat_0=-90 +ellps=WGS84 +no_defs"
)
ggplot() + geom_sf(data = world2)
}
# }
