ggmapcn (version 0.3.0)

basemap_dem: 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,
  ...
)

Value

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

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`.

See Also

geom_boundary_cn

Examples

# \donttest{
# 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()
# }