Display polygons as a map. This is meant as annotation, so it does not
affect position scales. Note that this function predates the geom_sf()
framework and does not work with sf geometry columns as input. However,
it can be used in conjunction with geom_sf()
layers and/or
coord_sf()
(see examples).
Usage
geom_map(
mapping = NULL,
data = NULL,
stat = "identity",
...,
map,
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE
)
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)
).- stat
The statistical transformation to use on the data for this layer, either as a
ggproto
Geom
subclass or as a string naming the stat stripped of thestat_
prefix (e.g."count"
rather than"stat_count"
)- ...
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.- map
Data frame that contains the map coordinates. This will typically be created using
fortify()
on a spatial object. It must contain columnsx
orlong
,y
orlat
, andregion
orid
.- 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()
.
Aesthetics
geom_map()
understands the following aesthetics (required aesthetics are in bold):
Learn more about setting these aesthetics in vignette("ggplot2-specs")
.
Examples
# First, a made-up example containing a few polygons, to explain
# how `geom_map()` works. It requires two data frames:
# One contains the coordinates of each polygon (`positions`), and is
# provided via the `map` argument. The other contains the
# other the values associated with each polygon (`values`). An id
# variable links the two together.
ids <- factor(c("1.1", "2.1", "1.2", "2.2", "1.3", "2.3"))
values <- data.frame(
id = ids,
value = c(3, 3.1, 3.1, 3.2, 3.15, 3.5)
)
positions <- data.frame(
id = rep(ids, each = 4),
x = c(2, 1, 1.1, 2.2, 1, 0, 0.3, 1.1, 2.2, 1.1, 1.2, 2.5, 1.1, 0.3,
0.5, 1.2, 2.5, 1.2, 1.3, 2.7, 1.2, 0.5, 0.6, 1.3),
y = c(-0.5, 0, 1, 0.5, 0, 0.5, 1.5, 1, 0.5, 1, 2.1, 1.7, 1, 1.5,
2.2, 2.1, 1.7, 2.1, 3.2, 2.8, 2.1, 2.2, 3.3, 3.2)
)
ggplot(values) +
geom_map(aes(map_id = id), map = positions) +
expand_limits(positions)
ggplot(values, aes(fill = value)) +
geom_map(aes(map_id = id), map = positions) +
expand_limits(positions)
ggplot(values, aes(fill = value)) +
geom_map(aes(map_id = id), map = positions) +
expand_limits(positions) + ylim(0, 3)
# Now some examples with real maps
if (require(maps)) {
crimes <- data.frame(state = tolower(rownames(USArrests)), USArrests)
# Equivalent to crimes %>% tidyr::pivot_longer(Murder:Rape)
vars <- lapply(names(crimes)[-1], function(j) {
data.frame(state = crimes$state, variable = j, value = crimes[[j]])
})
crimes_long <- do.call("rbind", vars)
states_map <- map_data("state")
# without geospatial coordinate system, the resulting plot
# looks weird
ggplot(crimes, aes(map_id = state)) +
geom_map(aes(fill = Murder), map = states_map) +
expand_limits(x = states_map$long, y = states_map$lat)
# in combination with `coord_sf()` we get an appropriate result
ggplot(crimes, aes(map_id = state)) +
geom_map(aes(fill = Murder), map = states_map) +
# crs = 5070 is a Conus Albers projection for North America,
# see: https://epsg.io/5070
# default_crs = 4326 tells coord_sf() that the input map data
# are in longitude-latitude format
coord_sf(
crs = 5070, default_crs = 4326,
xlim = c(-125, -70), ylim = c(25, 52)
)
ggplot(crimes_long, aes(map_id = state)) +
geom_map(aes(fill = value), map = states_map) +
coord_sf(
crs = 5070, default_crs = 4326,
xlim = c(-125, -70), ylim = c(25, 52)
) +
facet_wrap(~variable)
}