Area of spatial units

Calculate the area (or length) of each site in a spatial data set or phylospatial object. The main use of this function is to derive site weights for phylospatial(); see the site_weight argument of that function for details.

Usage

ps_area(x)

Arguments

x

A phylospatial object, a SpatRaster, or an sf object. Must have a defined coordinate reference system.

Value

A numeric vector with one value per site (including unoccupied sites, for a phylospatial object), giving area in square kilometers for raster cells and polygons, or length in kilometers for lines.

Details

Raster cell areas are calculated with cellSize, which accounts for variation in cell area across latitudes in longitude/latitude rasters. Polygon areas and line lengths are calculated with expanse and perim, respectively. Point sites have no area, so every point is given a value of 1.

See also

phylospatial()

Examples

# cells in a longitude/latitude raster shrink toward the poles
r <- terra::rast(nrows = 10, ncols = 10, xmin = -120, xmax = -100, ymin = 30, ymax = 60)
a <- ps_area(r)
range(a)
#> [1] 38957.86 63196.01

# one way to use these values as site weights:
comm <- terra::rast(r, nlyrs = 3)
names(comm) <- c("sp1", "sp2", "sp3")
set.seed(1)
comm[] <- rbinom(terra::ncell(comm) * 3, 1, .5)
tree <- ape::rtree(3, tip.label = names(comm))
ps <- phylospatial(comm, tree, site_weight = sqrt(a))
#> Community data type detected: binary