area function

Size of cells

Raster objects: Compute the approximate surface area of cells in an unprojected (longitude/latitude) Raster object. It is an approximation because area is computed as the height (latitudinal span) of a cell (which is constant among all cells) times the width (longitudinal span) in the (latitudinal) middle of a cell. The width is smaller at the poleward side than at the equator-ward side of a cell. This variation is greatest near the poles and the values are thus not very precise for very high latitudes.

SpatialPolygons: Compute the area of the spatial features. Works for both planar and angular (lon/lat) coordinate reference systems

## S4 method for signature 'RasterLayer'
area(x, filename="", na.rm=FALSE, weights=FALSE, ...)

## S4 method for signature 'RasterStackBrick'
area(x, filename="", na.rm=FALSE, weights=FALSE, ...)

## S4 method for signature 'SpatialPolygons'
area(x, ...)

Arguments

• x: Raster* or SpatialPolygons object
• filename: character. Filename for the output Raster object (optional)
• na.rm: logical. If TRUE, cells that are NA are ignored
• weights: logical. If TRUE, the area of each cells is divided by the total area of all cells that are not NA
• ...: additional arguments as for writeRaster

Details

If x is a RasterStack/Brick, a RasterBrick will be returned if na.rm=TRUE. However, if na.rm=FALSE, a RasterLayer is returned, because the values would be the same for all layers.

Returns

If x is a Raster* object: RasterLayer or RasterBrick. Cell values represent the size of the cell in km2, or the relative size if weights=TRUE. If the CRS is not longitude/latitude the values returned are the product of the cell resolution (typically in square meter).

If x is a SpatialPolygons* object: area of each spatial object in squared meters if the CRS is longitude/latitude, or in squared map units (typically meter)

Examples

r <- raster(nrow=18, ncol=36)
a <- area(r)

p <- shapefile(system.file("external/lux.shp", package="raster"))
p$area <- round(area(p) / 10000000,1)
p$area