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Elevation Map of China Layer for ggplot2

Source: R/basemap_dem.R
basemap_dem.Rd

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. If NULL (default), the function uses the built-in DEM data (gebco_2024.tif).

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.

See also

geom_boundary_cn

Examples

# Define Azimuthal Equidistant projection centered on China
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()
#> <SpatRaster> resampled to 1001520 cells.


# 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()
#> Warning: [vect] returning polygons ignoring additional geometry types. Use 'svc' to get all geometries
#> <SpatRaster> resampled to 1000968 cells.


# Example 3: Use custom DEM data by specifying the path to your DEM file
# dem_path <- "path/to/your/dem_file.tif" # Specify the path to your DEM file
dem_path <- system.file("extdata", "gebco_2024.tif", package = "ggmapcn") # Use the built-in DEM data
ggplot() +
  basemap_dem(data = terra::rast(dem_path), within_china = FALSE) +
  theme_minimal()
#> <SpatRaster> resampled to 1001520 cells.