Get the expanse (area) of individual polygons or for all (summed) raster cells
Compute the area covered by polygons or for all raster cells that are not NA.
This method computes areas for longitude/latitude rasters, as the size of the cells is constant in degrees, but not in meters. But it can also be important if the coordinate reference system is planar, but not equal-area.
For vector data, the best way to compute area is to use the longitude/latitude CRS. This is contrary to (erroneous) popular belief that suggest that you should use a planar coordinate reference system. This is done automatically, if transform=TRUE.
## S4 method for signature 'SpatRaster' expanse(x, unit="m", transform=TRUE) ## S4 method for signature 'SpatVector' expanse(x, unit="m", transform=TRUE)
x |
SpatRaster or SpatVector |
unit |
character. One of "m", "km", or "ha" |
transform |
logical. If |
numeric. The sum of the size of the cells that are not NA
### SpatRaster
r <- rast(nrow=18, ncol=36)
v <- 1:ncell(r)
v[200:400] <- NA
values(r) <- v
# summed area in km2
expanse(r, unit="km")
r <- rast(ncol=90, nrow=45, ymin=-80, ymax=80)
m <- project(r, "+proj=merc")
expanse(m, unit="km")
expanse(m, unit="km", transform=FALSE)
### SpatVector
v <- vect(system.file("ex/lux.shp", package="terra"))
a <- expanse(v)
a
sum(a)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.