How to add european countries borders to a Raster in R? - r

Question

I have this raster file:
fdiff_north:
class : RasterLayer
dimensions : 5500, 12000, 6.6e+07 (nrow, ncol, ncell)
resolution : 100, 100 (x, y)
extent : 4e+06, 5200000, 2250000, 2800000 (xmin, xmax, ymin, ymax)
crs : +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs
source : memory
names : layer
values : -1, 1 (min, max)
to get a plot:
cl <- colorRampPalette(c("red","white","blue"))(100)
plot(fdiff_north, col=cl)
I need boundaries to make the plot more usable.
I also tried to change the crs of my raster:
rfdiff_north:
class : RasterLayer
dimensions : 12571, 6151, 77324221 (nrow, ncol, ncell)
resolution : 9e-04, 0.00128 (x, y)
extent : 42.7836, 48.3195, 5.672145, 21.76303 (xmin, xmax, ymin, ymax)
crs : +proj=longlat +datum=WGS84 +no_defs
source : r_tmp_2022-02-07_151752_9872_54603.grd
names : layer
values : -1.466443, 1.366832 (min, max)
I want to add european countries boundaries to my raster, but I can't get it. I've tried with many different functions but I achieved no results. Can you help me to do that ?

Answer 1

The boundaries of European countries you can get from spMaps or any other source (OpenStreetMap data for example)
# devtools::install_github("rte-antares-rpackage/spMaps", ref = "master")
library(spMaps)
eu <- getEuropeCountries(mergeCountry = FALSE)
Trying to create similar (in size and CRS) raster:
library(terra)
#> terra 1.5.17
x <- rast(nrows=5500, ncols = 12000, nlyrs = 1,
xmin = 4e+06, xmax = 5200000, ymin = 2250000, ymax = 2800000,
crs = "+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs",
resolution = 100)
x <- setValues(x,runif(ncell(x)))
x
#> class : SpatRaster
#> dimensions : 5500, 12000, 1 (nrow, ncol, nlyr)
#> resolution : 100, 100 (x, y)
#> extent : 4e+06, 5200000, 2250000, 2800000 (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs
#> source : memory
#> name : lyr.1
#> min value : 4.889444e-09
#> max value : 1
Now it's time to convert SpatialPolygons to SimpleFeature and transform the coordinates to yours CRS:
library(sf)
eu <- st_as_sf(eu)
plot(x)
plot(st_transform(eu$geometry,
crs = "+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs"),
add = TRUE)
Created on 2022-02-09 by the reprex package (v2.0.1)
You can crop boundaries to your raster bbox with st_crop()
Regards,
Grzegorz