Set the map projection (CRS)

This function sets the map projection. It can also be set via tm_shape(), but tm_crs is generally recommended. It can also be determined automatically (see details); however, this is still work-in-progress.

Usage

tm_crs(crs = NA, property = NA)

Arguments

crs

Map projection (CRS). Can be set to an crs object (see sf::st_crs()), a proj4string, an EPSG number, or one the the following generic projections: c("laea", "aeqd", "utm", "pconic", "eqdc", "stere"). See details.

property

Which property should the projection have? One of: "global", "area" (equal-area), "distance" (equidistant), "shape" (conformal). Only applicable if crs = "auto". See details.

Details

The automatic crs recommendation is following:

Property	Recommendation
global (for world maps)	A pseudocylindrical projection tmap option crs_global, by default "eqearth (Equal Eearth). See https://r-tmap.github.io/tmap/articles/41_advanced_crs.html for more options
area (equal area)	Lambert Azimuthal Equal Area (laea)
distance (equidistant)	Azimuthal Equidistant (aeqd)
shape (conformal)	Stereographic (stere)

For further info about the available "generic" projects see: for utm: https://proj.org/en/9.4/operations/projections/utm.html for laea: https://proj.org/en/9.4/operations/projections/laea.html for aeqd: https://proj.org/en/9.4/operations/projections/aeqd.html for pconic: https://proj.org/en/9.4/operations/projections/pconic.html for eqdc: https://proj.org/en/9.4/operations/projections/eqdc.html

Note

Plans are to migrate the functionality regarding generic crs and automatic crs recommendation to a separate package.

Examples

SA = World[World$continent == "South America", ]

# latlon coordinates (WGS84)
tm_shape(SA) +
  tm_polygons() +
  tm_graticules() +
  tm_crs(4326)


tm_list = lapply(c("global", "area", "distance", "shape"), FUN = function(property) {
  tm_shape(SA) +
    tm_polygons() +
    tm_graticules() +
    tm_crs(property = property)  +
  tm_title(property)
})

tmap_arrange(tm_list, nrow = 1)