Polygons To Lines

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

The outlines of polygons as line features.

Pitfall. Shared edges between neighbouring polygons appear once per polygon unless the engine builds a topology.

About this operation
Also called	Polygon To Line, boundary, outline
Group	`vector/geometry`
Checks	`geometry.valid`
Pitfalls	1 listed above
Columbus tool	Not stated
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	`lines-to-polygons`

Parameters

Not stated

Inputs and outputs

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

In each engine

Engine	Tool	Parameters	Differences
`apache-sedona`	`sedona.sql.ST_Boundary`	`layer` → `geometry`	A Spark SQL function: arguments are columns or column names, run over a Spark DataFrame.
`geopandas`	`geopandas.GeoSeries.boundary`	Not stated	A property of the GeoSeries; returns a GeoSeries without the other columns.
`grass`	`v.type`	`layer` → `input` `output` → `output`	Converts area boundaries to lines; a boundary shared by two areas becomes one line, not one per polygon. Preset: `{"from_type":"boundary","to_type":"line"}`
`postgis`	`st_boundary`	`layer` → `#1`	None noted
`qgis`	`native:polygonstolines`	`layer` → `INPUT` `output` → `OUTPUT`	None noted
`sf`	`sf::st_boundary`	`layer` → `x`	None noted
`shapely`	`shapely.boundary`	`layer` → `geometry`	Also gives the end points of lines and nothing for points (the boundary in the OGC sense).
`turf-js`	`turf.polygonToLine`	`layer` → `poly`	One polygon (a Feature or geometry) per call, not a FeatureCollection. Turf works on GeoJSON in longitude/latitude (WGS 84); data in another CRS must be reprojected first.
`whiteboxtools`	`PolygonsToLines`	`layer` → `input` `output` → `output`	None noted

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