Random Points in Polygons

Draft: written, not yet checked by a person Operation · random-points-in-polygons

A given number of randomly placed points inside each polygon.

Pitfall. Some engines spread the count over the whole layer rather than placing it in each polygon.

Pitfall. Some return one multipoint per polygon rather than separate points.

About this operation
Also called	Create Random Points, random sample, generate points, sample points
Group	`vector/sampling`
Checks	`geometry.valid`
Pitfalls	2 listed above
Columbus tool	Not stated
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	`create-grid`

Parameters

Name	Type	Required	Default	Values	Note
`count`	integer	yes	Not stated	Not stated	Points per polygon.
`seed`	integer	no	Not stated	Not stated	A seed for the random numbers, so a run can be repeated.

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

Engine	Tool	Parameters	Differences
`geopandas`	`geopandas.GeoSeries.sample_points`	`count` → `size` `seed` → `rng`	Returns one MultiPoint per row; method can also use pointpats' cluster processes.
`grass`	`v.random`	`count` → `npoints` `seed` → `seed` `layer` → `restrict` `output` → `output`	npoints is the total for the region or the restricting areas unless flag a puts that many in each area; this mapping sets a. Preset: `{"flag_a":true}`
`postgis`	`st_generatepoints`	`count` → `#2` `seed` → `#3` `layer` → `#1`	Returns one MultiPoint per polygon.
`qgis`	`native:randompointsinpolygons`	`count` → `POINTS_NUMBER` `seed` → `SEED` `layer` → `INPUT` `output` → `OUTPUT`	INCLUDE_POLYGON_ATTRIBUTES (on by default) copies the polygon's attributes, including a GeoPackage's fid, so writing the points to a GeoPackage fails on duplicate fids; turn it off or write another format. MIN_DISTANCE keeps points apart; it may place fewer points when they do not fit.
`sf`	`sf::st_sample`	`count` → `size` `seed` Call set.seed() first; there is no seed argument. `layer` → `x`	size is the total over all polygons, shared by area, unless given one value per polygon.
`terra`	`terra::spatSample`	`count` → `size` `seed` Call set.seed() first; there is no seed argument. `layer` → `x`	For polygons, size is the total over the layer; strata can spread it by polygon.