Measure Area

Draft: written, not yet checked by a person Operation · measure-area

The area of each polygon, as a number or a new attribute.

Pitfall. In a geographic CRS, planar engines return square degrees; geodesic ones (Turf, terra, PostGIS geography) return square metres.

Pitfall. Projected areas carry the projection's scale error; use an equal-area projection for large areas.

About this operation
Also called	Calculate Geometry (area), Add Geometry Attributes, polygon area, shape area
Group	`vector/measure`
Checks	`crs.measure`
Pitfalls	2 listed above
Columbus tool	Not stated
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	`measure-length`

Parameters

Name	Type	Required	Default	Values	Note
`unit`	enum	no	`m2`	`m2, ha, km2, ft2, acre`	Not stated

Inputs and outputs

Direction	Name	Type	Geometry	Note
Input	`layer`	vector	polygon	Not stated
Output	`output`	any	Not stated	The areas, or the layer with an area attribute.

In each engine

Engine	Tool	Parameters	Differences
`apache-sedona`	`sedona.sql.ST_Area`	`unit` always crs-units. Square CRS units (square metres in a metric CRS); convert afterwards for other units. `layer` → `geometry`	A Spark SQL function: arguments are columns or column names, run over a Spark DataFrame.
`geopandas`	`geopandas.GeoSeries.area`	`unit` always crs-units. Square CRS units (square metres in a metric CRS); convert afterwards for other units.	A property of the GeoSeries; warns when the CRS is geographic.
`grass`	`v.to.db`	`unit` → `units` : m2 = meters; km2 = kilometers; ha = hectares; acre = acres; ft2 = feet `layer` → `map`	Writes into the map's own attribute table (the column must exist; this mapping names it area); option also gives length, perimeter, coordinates and more. Preset: `{"option":"area","columns":"area"}`
`postgis`	`st_area`	`unit` always crs-units. Square CRS units (square metres in a metric CRS); convert afterwards for other units. `layer` → `#1`	On geography, square metres on the spheroid (use_spheroid).
`qgis`	`native:exportaddgeometrycolumns`	`unit` always crs-units. Square CRS units (square metres in a metric CRS); convert afterwards for other units. `layer` → `INPUT` `output` → `OUTPUT`	Adds area and perimeter fields to polygons (length to lines, coordinates to points); METHOD 2 measures on the ellipsoid.
`sf`	`sf::st_area`	`unit` always crs-units. Square CRS units (square metres in a metric CRS); convert afterwards for other units. `layer` → `x`	Returns a units object; on longitude/latitude data, square metres on the sphere or ellipsoid.
`shapely`	`shapely.area`	`unit` always crs-units. Square CRS units (square metres in a metric CRS); convert afterwards for other units. `layer` → `geometry`	None noted
`terra`	`terra::expanse`	`unit` → `unit` : m2 = m; km2 = km; ha = ha. not supported: ft2, acre `layer` → `x`	Square metres even for longitude/latitude data (geodesic); also measures raster cell areas.
`turf-js`	`turf.area`	`unit` always m2. Always square metres (geodesic). `layer` → `geojson`	One total for all features of a FeatureCollection. Turf works on GeoJSON in longitude/latitude (WGS 84); data in another CRS must be reprojected first.
`whiteboxtools`	`PolygonArea`	`unit` always crs-units. Square CRS units (square metres in a metric CRS); convert afterwards for other units. `layer` → `input`	Adds an AREA field to the input file itself; there is no separate output.