Simplify

Draft: written, not yet checked by a person Operation · simplify

Removes vertices from lines and polygon outlines within a tolerance, keeping their overall shape.

Pitfall. Simplifying polygons one at a time can open gaps and overlaps between neighbours that shared an edge.

About this operation
Also called	Simplify Line, Simplify Polygon, generalize, Douglas-Peucker
Group	`vector/geometry`
Checks	`crs.measure, geometry.valid`
Pitfalls	1 listed above
Columbus tool	`vector_op · simplify`
Notes	Not stated
Status	active
Broader	Not stated
Narrower	Not stated
Related	Not stated

Parameters

Name	Type	Required	Default	Values	Note
`tolerance`	length	yes	Not stated	Not stated	Not stated
`unit`	enum	yes	Not stated	`m, ft, us-ft, km, mi`	Not stated
`preserve_topology`	boolean	no	`yes`	Not stated	Avoid creating invalid or collapsed shapes.

Inputs and outputs

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

In each engine

Engine	Tool	Parameters	Differences
`apache-sedona`	`sedona.sql.ST_Simplify`	`tolerance` → `distance_tolerance` `unit` always crs-units `preserve_topology` always no. Use ST_SimplifyPreserveTopology. `layer` → `geometry`	A Spark SQL function: arguments are columns or column names, run over a Spark DataFrame.
`apache-sedona`	`sedona.sql.ST_SimplifyPreserveTopology`	`tolerance` → `distance_tolerance` `unit` always crs-units `preserve_topology` always yes. Use ST_Simplify to simplify without preserving topology. `layer` → `geometry`	A Spark SQL function: arguments are columns or column names, run over a Spark DataFrame.
`gdal`	`gdal vector simplify`	`tolerance` → `tolerance` `unit` always crs-units. Tolerance is in the layer's CRS units; convert it first. `preserve_topology` always yes `layer` → `input` `output` → `output`	None noted
`geopandas`	`geopandas.GeoSeries.simplify`	`tolerance` → `tolerance` `unit` always crs-units. Tolerance is in the series' CRS units; convert it first. `preserve_topology` → `preserve_topology`	None noted
`grass`	`v.generalize`	`tolerance` → `threshold` `unit` always crs-units. Threshold is in the map units of the GRASS project. `layer` → `input` `output` → `output`	Offers many other methods (reduction, Lang, Reumann-Witkam, smoothing); this mapping uses Douglas-Peucker. Preset: `{"method":"douglas"}`
`postgis`	`st_simplify`	`tolerance` → `#2` `unit` always crs-units `preserve_topology` always no. Use ST_SimplifyPreserveTopology to keep topology. `layer` → `#1`	Can return invalid or collapsed geometries; the optional third argument keeps collapsed ones.
`postgis`	`st_simplifypreservetopology`	`tolerance` → `#2` `unit` always crs-units `preserve_topology` always yes. Use ST_Simplify when topology need not be kept. `layer` → `#1`	None noted
`qgis`	`native:simplifygeometries`	`tolerance` → `TOLERANCE` `unit` always crs-units. Tolerance is in the layer's CRS units; convert it first. `layer` → `INPUT` `output` → `OUTPUT`	METHOD also offers snap-to-grid and Visvalingam (area) simplification; this mapping uses Douglas-Peucker. Preset: `{"METHOD":0}`
`sf`	`sf::st_simplify`	`tolerance` → `dTolerance` `unit` always crs-units. Projected data: CRS units. Longitude/latitude data with sf_use_s2() on: metres (S2's simplify). `preserve_topology` → `preserveTopology` `layer` → `x`	preserveTopology has no default; it is ignored for longitude/latitude data simplified through S2.
`shapely`	`shapely.simplify`	`tolerance` → `tolerance` `unit` always crs-units. Shapely has no CRS; tolerance is in the coordinates' units. `preserve_topology` → `preserve_topology` `layer` → `geometry`	None noted
`terra`	`terra::simplifyGeom`	`tolerance` → `tolerance` `unit` always crs-units `preserve_topology` → `preserveTopology` `layer` → `x`	Repairs invalid results by default (makeValid = TRUE).
`turf-js`	`turf.simplify`	`tolerance` → `options.tolerance` `unit` always crs-units. The tolerance is in degrees. `preserve_topology` always no `layer` → `geojson`	tolerance defaults to 1 (degree); highQuality uses the slower full Douglas-Peucker without radial-distance prefiltering. Turf works on GeoJSON in longitude/latitude (WGS 84); data in another CRS must be reprojected first.