Raster To Polygons

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

Turns areas of connected cells with the same value into polygons, each carrying that value.

Pitfall. Continuous rasters (elevation, imagery) give one polygon per cell or tiny group of cells; classify or round values first.

Pitfall. Engines differ on floating-point values; some truncate them to integers first.

About this operation
Also called	Polygonize, Raster To Polygon, raster to vector, vectorize
Group	`conversion/raster-to-vector`
Checks	`raster.nodata, geometry.valid`
Pitfalls	2 listed above
Columbus tool	Not stated
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	`rasterize`

Parameters

Name	Type	Required	Default	Values	Note
`band`	integer	no	`1`	Not stated	Not stated
`field`	string	no	Not stated	Not stated	Name of the attribute that holds each polygon's cell value.
`eight_connected`	boolean	no	`no`	Not stated	Join cells that touch only at a corner (8-connectedness) instead of only along edges.

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

Engine	Tool	Parameters	Differences
`gdal`	`gdal raster polygonize`	`band` → `band` `field` → `attribute-name` `eight_connected` → `connect-diagonal-pixels` `raster` → `input` `output` → `output`	None noted
`grass`	`r.to.vect`	`field` → `column` `raster` → `input` `output` → `output`	None noted Preset: `{"type":"area"}`
`postgis-raster`	`st_dumpaspolygons`	`band` → `band` `raster` → `rast`	Returns a set of (geom, val) rows.
`qgis`	`gdal:polygonize`	`band` → `BAND` `field` → `FIELD` `eight_connected` → `EIGHT_CONNECTEDNESS` `raster` → `INPUT` `output` → `OUTPUT`	None noted
`rasterio`	`rasterio.features.shapes`	`eight_connected` → `connectivity` : false = 4; true = 8 `raster` → `source`	A generator of (GeoJSON geometry, value) pairs from an array; pass the raster's transform to get map coordinates.
`terra`	`terra::as.polygons`	`eight_connected` always no `raster` → `x`	With aggregate = TRUE (the default) all cells with the same value become one polygon, connected or not.
`whiteboxtools`	`RasterToVectorPolygons`	`raster` → `input` `output` → `output`	None noted