Unexpected warning when plotting geom_map()

[edgararuiz-zz]

reprex:

library(ggplot2)
wr <- map_data("world")
ggplot() +
  geom_map(aes(long, lat, map_id = region), map = wr, data = wr)
#> Warning: Ignoring unknown aesthetics: x, y

[paleolimbot]

I think the problem is that GeomMap inherits from GeomPolygon but overrides required_aes, which should probably be c("map_id", "x", "y").

ggplot2/R/geom-map.r

Lines 118 to 122 in d1ecd03

	)
	},
	required_aes = c("map_id")
	)

[yutannihilation]

I don't know well about geom_map(), but isn't the warning right? With goem_map(), you cannot map variables in the usual plot/layer data to x and y; you need to pass a separate data to map argument and aes() does nothing there.

For example, if the data doesn't have a column named x or long, it fails.

library(ggplot2)
wr <- map_data("world")
wr <- dplyr::rename(wr, lon = long)

ggplot() +
  geom_map(aes(lat, lon, map_id = region), map = wr, data = wr2)
#> Error in geom_map(aes(lat, lon, map_id = region), map = wr, data = wr2): all(c("x", "y", "id") %in% names(map)) is not TRUE

^{Created on 2019-08-19 by the reprex package (v0.3.0)}

[yutannihilation]

Now that we have setup_data(), maybe we can issue a bit friendlier warning when x or y is mapped accidentally?

[clauswilke]

I don't understand this issue. Reading the documentation of geom_map() (which arguable is rather lacking and unclear), the code posted with this issue is incorrect, and the warning is correct. geom_map() ignores the x and y aesthetics, as the warning says.

The correct way to set the limits is via expand_limits(), like so:

library(ggplot2)
wr <- map_data("world")
ggplot() +
  geom_map(aes(map_id = region), map = wr, data = wr) +
  expand_limits(x = wr$long, y = wr$lat)

^{Created on 2019-12-19 by the reprex package (v0.3.0)}

[yutannihilation]

Yes, the warning is definitely correct. I meant adding some check like below might help the user find what they should do.

  ignoring_aes <- intersect(names(mapping), c("x", "y", "group"))
  if (length(ignoring_aes) > 0) {
    warn(glue("geom_map() doesn't accept mapping of `x`, `y`, or `group`, ",
              "but expects the data has fixed names of columns `x`, `y` and `id`."))
  }

What do you think? I'm OK to close this issue if there's no chance to improve the warning than simple Ignoring unknown aesthetics.

[clauswilke]

My concern about the warning is that the warning needs to be evaluated on the specific combination of geom and stat. Are there cases where somebody uses geom_map() with a different stat that can process x and y?

It seems to me that it would be more important to improve the documentation of geom_map() than to add this warning, because the current documentation barely explains anything. And also, we should discourage use of geom_map() in favor of geom_sf(), and we may want to add a sentence to this effect to the documentation.

[yutannihilation]

Sorry, I forgot to reply here. Thanks, agreed. I didn't think of the case...

And also, we should discourage use of geom_map() in favor of geom_sf(), and we may want to add a sentence to this effect to the documentation.

Sounds good. I've been wondered the status of geom_map().

[thomasp85]

I'm closing this in favour of #3721