geom_mapcn: Plot China Map with Customizable Options

In ggmapcn: Customizable China and Global Map Visualizations

Plot China Map with Customizable Options

Description

‘geom_mapcn()' draws China’s administrative units with a simple, opinionated interface. When 'data' is 'NULL', it loads packaged map data for the requested administrative level, optionally applies attribute-based filtering, removes internal clipping rows, and reprojects the layer to the target CRS.

In typical use, 'geom_mapcn()' is combined with 'geom_boundary_cn()' to draw coastlines, national borders, and other boundary features on top of the administrative polygons.

Usage

geom_mapcn(
  data = NULL,
  admin_level = "province",
  crs = "+proj=aeqd +lat_0=35 +lon_0=105 +ellps=WGS84 +units=m +no_defs",
  color = "black",
  fill = "white",
  linewidth = 0.1,
  filter_attribute = NULL,
  filter = NULL,
  mapping = NULL,
  ...
)

Arguments

data	An 'sf' object with geometries to draw. If 'NULL', the function loads the packaged dataset corresponding to 'admin_level'.
admin_level	Administrative level to plot. One of '"province"' (default), '"city"', or '"county"'. These map to packaged files 'China_sheng.rda', 'China_shi.rda', and 'China_xian.rda', respectively.
crs	Coordinate reference system used for plotting. Defaults to an azimuthal equidistant projection centered on China: '"+proj=aeqd +lat_0=35 +lon_0=105 +ellps=WGS84 +units=m +no_defs"'. Accepts PROJ strings or EPSG codes (e.g., '"EPSG:4326"').
color	Border color for polygons. Default '"black"'.
fill	Fill color for polygons. Default '"white"'.
linewidth	Border line width. Default '0.1'. For older 'ggplot2' versions, use 'size' instead of 'linewidth'.
filter_attribute	Optional name of an attribute column used to filter features (e.g., '"name_en"').
filter	Optional character vector of values to keep in 'filter_attribute' (e.g., 'c("Beijing", "Shanghai")'). If supplied together with 'filter_attribute', features are subsetted accordingly. If no features remain after filtering, an error is thrown.
mapping	Optional aesthetics mapping passed to 'ggplot2::geom_sf()'. This is useful when additional aesthetics (e.g., 'fill') should be mapped from columns in 'data'.
...	Additional arguments forwarded to 'ggplot2::geom_sf()'.

Details

If 'data' is 'NULL', 'geom_mapcn()' selects one of the packaged datasets:

* 'admin_level = "province"' → 'China_sheng.rda' * 'admin_level = "city"' → 'China_shi.rda' * 'admin_level = "county"' → 'China_xian.rda'

The file is ensured to exist locally via 'check_geodata()', which may reuse an existing copy in the package 'extdata' directory or user cache, or download it from the external repository when necessary. The '.rda' file is then loaded from the resolved path, and the main 'sf' object is extracted.

A special row labelled '"Boundary Line"' (used for technical clipping) is removed automatically when present. Attribute-based filtering can be applied using 'filter_attribute' and 'filter' before reprojecting to the target CRS.

Value

A 'ggplot2' layer that can be added to a plot.

Examples

# 1. Basic provincial map (recommended: combine with geom_boundary_cn)
ggplot() +
  geom_mapcn() +
  geom_boundary_cn() +
  theme_minimal()

# 2. City-level map with custom fill and boundaries
ggplot() +
  geom_mapcn(
    admin_level = "city",
    fill = "grey95",
    color = "grey60"
  ) +
  geom_boundary_cn(province_color = "grey40") +
  theme_bw()

# 3. Filter by attribute (e.g., English names) and highlight selected provinces
ggplot() +
  geom_mapcn(
    filter_attribute = "name_en",
    filter = c("Beijing", "Shanghai"),
    fill = "tomato"
  ) +
  geom_boundary_cn() +
  theme_minimal()

# 4. Use a different projection (e.g., Albers equal-area)
albers_cn <- "+proj=aea +lat_1=25 +lat_2=47 +lat_0=0 +lon_0=105 +datum=WGS84"

ggplot() +
  geom_mapcn(crs = albers_cn, linewidth = 0.3) +
  geom_boundary_cn(crs = albers_cn) +
  coord_sf(crs = albers_cn) +
  theme_minimal()

ggmapcn documentation built on Nov. 23, 2025, 9:06 a.m.