Coordinate System with Transformed Limits for Custom Projections

coord_proj is a wrapper around ggplot2::coord_sf(). It simplifies specifying map limits (xlim, ylim) in longitude and latitude (WGS84 CRS) and automatically transforms them into the specified CRS for accurate projections.

This function extends the functionality of coord_sf() to seamlessly handle user-specified geographic boundaries in any projection, ensuring accurate mapping.

Usage

coord_proj(
  crs = NULL,
  xlim = NULL,
  ylim = NULL,
  expand = TRUE,
  default_crs = "EPSG:4326",
  ...
)

Arguments

crs

A character string specifying the coordinate reference system (CRS) for the projection (e.g., "EPSG:4326" or custom projections like "+proj=merc").

xlim

Longitude range (in degrees) to display, as a numeric vector of length 2.

ylim

Latitude range (in degrees) to display, as a numeric vector of length 2.

expand

Logical, whether to expand the plot limits. Default is TRUE.

default_crs

A character string specifying the CRS of the input xlim and ylim. Default is "EPSG:4326".

...

Additional arguments passed to ggplot2::coord_sf().

Value

A ggplot2 coord_sf object with the transformed limits.

See also

ggplot2::coord_sf, geom_world

Examples

# World map with default projection and limits
ggplot() +
  geom_world() +
  coord_proj(
    crs = "+proj=longlat +datum=WGS84",
    xlim = c(-180, 180),
    ylim = c(-90, 90),
    expand=FALSE
  ) +
  theme_minimal()
#> Linking to GEOS 3.11.2, GDAL 3.8.2, PROJ 9.3.1; sf_use_s2() is TRUE


# Focused view with Azimuthal Equidistant projection
china_proj <- "+proj=aeqd +lat_0=35 +lon_0=105 +ellps=WGS84 +units=m +no_defs"
ggplot() +
  geom_world(fill = "lightblue") +
  coord_proj(
    crs = china_proj,
    xlim = c(60, 140),
    ylim = c(-10, 50)
  ) +
  theme_minimal()


# Display a small map of the South China Sea Islands with a custom projection
ggplot() +
  geom_boundary_cn() +
  theme_bw() +
  coord_proj(
    crs = china_proj,
    expand = FALSE,
    xlim = c(105, 123),
    ylim = c(2, 23)
  )