Lines To Polygons

Draft: written, not yet checked by a person Operation · lines-to-polygons

Polygons formed by closed lines, or by the areas that a network of lines encloses.

Pitfall. Some engines turn each closed line into a polygon; others build polygons from every area the lines enclose together, which differs when lines cross.

Pitfall. Lines that do not quite meet (an unsnapped gap) enclose nothing.

About this operation
Also called	Feature To Polygon, polygonize lines, close rings
Group	`vector/geometry`
Checks	`geometry.valid`
Pitfalls	2 listed above
Columbus tool	Not stated
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	`polygons-to-lines` `raster-to-polygons`

Parameters

Not stated

Inputs and outputs

Direction	Name	Type	Geometry	Note
Input	`layer`	vector	line	Not stated
Output	`output`	vector	polygon	Not stated

In each engine

Engine	Tool	Parameters	Differences
`geopandas`	`geopandas.GeoSeries.polygonize`	Not stated	Builds polygons from the areas the lines enclose together (noded first by default).
`postgis`	`st_polygonize`	`layer` → `#1`	An aggregate; returns one GeometryCollection of the enclosed areas.
`qgis`	`qgis:linestopolygons`	`layer` → `INPUT` `output` → `OUTPUT`	Closes each line into its own polygon (native:polygonize instead builds polygons from the areas lines enclose together).
`sf`	`sf::st_polygonize`	`layer` → `x`	Per feature; returns a GeometryCollection for each.
`shapely`	`shapely.polygonize`	`layer` → `geometries`	Builds polygons from the areas the lines enclose together; returns one GeometryCollection.
`turf-js`	`turf.polygonize`	`layer` → `geoJson`	Turf works on GeoJSON in longitude/latitude (WGS 84); data in another CRS must be reprojected first.
`whiteboxtools`	`LinesToPolygons`	`layer` → `input` `output` → `output`	None noted