basemap_dem: Elevation Map of China Layer for ggplot2

In ggmapcn: Customizable China Map Visualizations

Elevation Map of China Layer for ggplot2

Description

'basemap_dem' adds a digital elevation model (DEM) raster map of China as a layer to ggplot2. The function ensures the output map remains rectangular, regardless of the chosen projection. It supports displaying the DEM either within China's boundary or in a larger rectangular area around China. Users can provide their own DEM data using the 'data' parameter, or the default built-in DEM data will be used.

Usage

basemap_dem(
  data = NULL,
  crs = NULL,
  within_china = FALSE,
  maxcell = 1e+06,
  na.rm = FALSE,
  ...
)

Arguments

data	Optional. A 'terra' raster object for custom DEM data.
crs	Coordinate reference system (CRS) for the projection. Defaults to the CRS of the DEM data. Users can specify other CRS strings (e.g., '"EPSG:4326"' or custom projections).
within_china	Logical. If ‘TRUE', displays only the DEM within China’s boundary. If 'FALSE', displays the DEM for a larger rectangular area around China. Default is 'FALSE'.
maxcell	Maximum number of cells for rendering (to improve performance). Defaults to '1e6'.
na.rm	Logical. If 'TRUE', removes missing values. Default is 'FALSE'.
...	Additional parameters passed to 'geom_spatraster'.

Value

A 'ggplot' object containing the elevation map of China as a layer, which can be further customized or plotted.

See Also

geom_boundary_cn

Examples

# Before using the basemap_dem function, make sure the required data files are available.
# The required files are: "gebco_2024_China.tif" and "China_mask.gpkg".
# You can use check_geodata() to download them from GitHub if they are not available locally.

# Check and download the required data files if they are missing
check_geodata(files = c("gebco_2024_China.tif", "China_mask.gpkg"))

# Define the CRS for China (EPSG:4326 is a common global geographic coordinate system)
china_proj <- "+proj=aeqd +lat_0=35 +lon_0=105 +ellps=WGS84 +units=m +no_defs"

# Example 1: Display full rectangular area around China using built-in DEM data
ggplot() +
  basemap_dem(within_china = FALSE) +
  tidyterra::scale_fill_hypso_tint_c(
    palette = "gmt_globe",
    breaks = c(-10000, -5000, 0, 2000, 5000, 8000)
  ) +
  theme_minimal()

# Example 2: Display only China's DEM and boundaries using built-in DEM data
ggplot() +
  basemap_dem(crs = china_proj, within_china = TRUE) +
  geom_boundary_cn(crs = china_proj) +
  tidyterra::scale_fill_hypso_c(
    palette = "dem_print",
    breaks = c(0, 2000, 4000, 6000),
    limits = c(0, 7000)
  ) +
  labs(fill = "Elevation (m)") +
  theme_minimal()

ggmapcn documentation built on April 12, 2025, 2:09 a.m.