Different behaviour of scales param `na.value = NA` in `geom_tile()` and `geom_raster()`

[dieghernan]

HI:

Following an issue on tidyterra (dieghernan/tidyterra#120, see also https://stackoverflow.com/questions/77474839/ggplot-of-raster-maps-horizontal-vertical-grid-cells-distortion/77486091#77486091) I think the root cause may be on how ggplot2 handles the param na.value = NA on geom_raster() (note that geom_spatraster() is leveraging on this ggplot2 function). See the different behaviour compared with geom_tile():

ex <- tibble::tribble(
  ~x, ~y, ~ExampleMap2,
  4415000L, 2865000L, 1L,
  4425000L, 2865000L, NA,
  4435000L, 2865000L, NA,
  4445000L, 2865000L, NA,
  4415000L, 2855000L, NA,
  4425000L, 2855000L, NA,
  4435000L, 2855000L, NA,
  4445000L, 2855000L, NA,
  4415000L, 2845000L, 1L,
  4425000L, 2845000L, NA,
  4435000L, 2845000L, NA,
  4445000L, 2845000L, NA,
  4415000L, 2835000L, NA,
  4425000L, 2835000L, NA,
  4435000L, 2835000L, NA,
  4445000L, 2835000L, NA,
  4415000L, 2825000L, 1L,
  4425000L, 2825000L, NA,
  4435000L, 2825000L, NA,
  4445000L, 2825000L, 1L
)

library(ggplot2)

p_raster <- ggplot(ex, aes(x, y)) +
  geom_raster(aes(fill = ExampleMap2)) +
  coord_equal()

# As expected
p_raster

# With na.value = NA extra cells are filled
p_raster +
  scale_fill_viridis_c(na.value = NA)
#> Warning: Removed 16 rows containing missing values (`geom_raster()`).

# Not happening with geom_tile
ggplot(ex, aes(x, y)) +
  geom_tile(aes(fill = ExampleMap2)) +
  coord_equal() +
  scale_fill_viridis_c(na.value = NA)

^{Created on 2023-11-15 with reprex v2.0.2}

[teunbrand]

Is this the same as #3025?
In any case, I think this particular example may also be solved by setting na.value = "transparent".
The fill is a non-missing aesthetic in geom_raster(), meaning that rows that have NA fills will be removed. Subsequently, there are too few cells to reconstruct the resolution of the data.

[dieghernan]

Hi,

Yes, it seems to be the same case, thanks for pointing out. transparent would do the trick:

ex <- tibble::tribble(
  ~x, ~y, ~ExampleMap2,
  4415000L, 2865000L, 1L,
  4425000L, 2865000L, NA,
  4435000L, 2865000L, NA,
  4445000L, 2865000L, NA,
  4415000L, 2855000L, NA,
  4425000L, 2855000L, NA,
  4435000L, 2855000L, NA,
  4445000L, 2855000L, NA,
  4415000L, 2845000L, 1L,
  4425000L, 2845000L, NA,
  4435000L, 2845000L, NA,
  4445000L, 2845000L, NA,
  4415000L, 2835000L, NA,
  4425000L, 2835000L, NA,
  4435000L, 2835000L, NA,
  4445000L, 2835000L, NA,
  4415000L, 2825000L, 1L,
  4425000L, 2825000L, NA,
  4435000L, 2825000L, NA,
  4445000L, 2825000L, 1L
)

library(ggplot2)

p_raster <- ggplot(ex, aes(x, y)) +
  geom_raster(aes(fill = ExampleMap2)) +
  coord_equal()

# As expected
p_raster

# Filling extra cells
p_raster +
  scale_fill_viridis_c(na.value = NA)
#> Warning: Removed 16 rows containing missing values (`geom_raster()`).

# Not happening with transparent
p_raster +
  scale_fill_viridis_c(na.value = "transparent")

^{Created on 2023-11-15 with reprex v2.0.2}