Look up the properties of the projections world_map() understands: the
construction family, whether it is equal-area (a choropleth's ink is
proportional to ground area) or conformal (shapes are locally right), and the
PROJ string the package builds. Called with no arguments it returns the whole
table, which is the quickest way to see what is available.
Value
A tibble with one row per projection: projection, family,
property, equal_area, conformal, note and proj4.
Choosing one
For a world choropleth the honest choice is equal-area, because the eye
reads coloured area as quantity: a projection that inflates Greenland makes
Greenland's value look more important than it is. Equal Earth is the
recommended default (and the package's own) – it is equal-area, close to
Robinson in appearance, and cheap to evaluate (Savric, Patterson & Jenny
2019). "mercator" is conformal, not equal-area, and should not be used for
choropleths. Use projection_compare() to see the difference on your own
data, and tissot_map() to see it on the graticule.
References
Savric, B., Patterson, T. & Jenny, B. (2019). The Equal Earth map projection. International Journal of Geographical Information Science 33(3), 454-465. doi:10.1080/13658816.2018.1504949
Examples
projection_info()
#> # A tibble: 13 × 7
#> projection family property equal_area conformal note proj4
#> <chr> <chr> <chr> <lgl> <lgl> <chr> <chr>
#> 1 equal_earth pseudocylindr… equal-a… TRUE FALSE Reco… +pro…
#> 2 robinson pseudocylindr… comprom… FALSE FALSE Neit… +pro…
#> 3 mollweide pseudocylindr… equal-a… TRUE FALSE Equa… +pro…
#> 4 natural_earth pseudocylindr… comprom… FALSE FALSE Comp… +pro…
#> 5 plate_carree cylindrical equidis… FALSE FALSE Equi… +pro…
#> 6 mercator cylindrical conform… FALSE TRUE Conf… +pro…
#> 7 winkel_tripel pseudoazimuth… comprom… FALSE FALSE Comp… +pro…
#> 8 eckert4 pseudocylindr… equal-a… TRUE FALSE Equa… +pro…
#> 9 gall_peters cylindrical equal-a… TRUE FALSE Equa… +pro…
#> 10 orthographic azimuthal perspec… FALSE FALSE A vi… +pro…
#> 11 azimuthal_equal_area azimuthal equal-a… TRUE FALSE Equa… +pro…
#> 12 north_polar azimuthal equal-a… TRUE FALSE Lamb… +pro…
#> 13 south_polar azimuthal equal-a… TRUE FALSE Lamb… +pro…
projection_info("mercator")
#> # A tibble: 1 × 7
#> projection family property equal_area conformal note proj4
#> <chr> <chr> <chr> <lgl> <lgl> <chr> <chr>
#> 1 mercator cylindrical conformal FALSE TRUE Conformal, and fa… +pro…
# every equal-area projection the package can build
subset(projection_info(), equal_area)$projection
#> [1] "equal_earth" "mollweide" "eckert4"
#> [4] "gall_peters" "azimuthal_equal_area" "north_polar"
#> [7] "south_polar"