Support `sf` objects for maps?

Hi @grantmcdermott, @vincentarelbundock and @zeileis, I'm just wondering whether support for sf objects is on the roadmap. ggplot2 can be quite slow when drawing maps with several elements (say all the US counties + fill by variable + points). To clarify, creating the map is not slow but printing it can easily take 15-20 seconds or more and I'm wondering if a base plot would be faster for this.

A complete support would probably be complicated, but here's a very simple example:

library(ggplot2)
library(sf)
#> Linking to GEOS 3.12.1, GDAL 3.8.4, PROJ 9.3.1; sf_use_s2() is TRUE

nc <- sf::st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)

ggplot(nc) +
  geom_sf(aes(fill = AREA))

nc[, "AREA", drop = FALSE] |> 
  plot()

Being able to do plt(~ AREA, fill = "by", type = "map") would be great (contrarily to the syntax for density plots, we'd only need to have one variable in the formula here).

Start with the supplied R examples and review the plt() entry point, especially formula handling and the fill and type arguments. Compare the requested sf map workflow with the existing base plotting path; done would mean a defined scope for sf support and a working way to use one formula variable with fill="by" and type="map".