simplify

simplifyGeometry

Signature

simplifyGeometry (geometry, options)

Description

Simplifies all coordinate sequences of a GeoJSON geometry using the Visvalingam-Whyatt algorithm. Supports LineString, Polygon, MultiLineString, MultiPolygon, and GeometryCollection. Point and MultiPoint geometries are returned unchanged. The operation is performed in place — the original object is mutated and returned.

Parameters

Name	Type	Required	Description
geometry	object	yes	A GeoJSON geometry object
options.tolerance	number	no	Minimum triangle area threshold below which a point is removed (default: 0)
options.getWeight	function	no	A function (coord, index) => number that returns a weight multiplied by the triangle area of each point. Defaults to () => 1 (no weighting)

Returns

Type	Description
object	The mutated geometry

Throws

Throws if geometry is not a valid GeoJSON geometry.

Examples

// LineString
simplifyGeometry(
  { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0.02],[3,0.01],[4,0]] },
  { tolerance: 1e-4 }
)
// { type: 'LineString', coordinates: [[0,0],[4,0]] }

// Polygon — each ring is simplified independently
simplifyGeometry(
  { type: 'Polygon', coordinates: [[[0,0],[1,0.01],[2,0],[3,0.01],[4,0],[2,-1],[0,0]]] },
  { tolerance: 1e-4 }
)
// { type: 'Polygon', coordinates: [[[0,0],[4,0],[2,-1],[0,0]]] }

// GeometryCollection — recurses into each geometry
simplifyGeometry(
  {
    type: 'GeometryCollection',
    geometries: [
      { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0]] },
      { type: 'LineString', coordinates: [[3,0],[4,0.01],[5,0]] }
    ]
  },
  { tolerance: 1e-4 }
)
// {
//   type: 'GeometryCollection',
//   geometries: [
//     { type: 'LineString', coordinates: [[0,0],[2,0]] },
//     { type: 'LineString', coordinates: [[3,0],[5,0]] }
//   ]
// }

// Point — returned unchanged
simplifyGeometry({ type: 'Point', coordinates: [2.3522, 48.8566] }, { tolerance: 1e-4 })
// { type: 'Point', coordinates: [2.3522, 48.8566] }

// Custom weight — preserve points of interest regardless of their area
simplifyGeometry(
  { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0.01],[3,0.01],[4,0]] },
  {
    tolerance: 1e-4,
    getWeight: (coord) => coord[0] === 2 ? 1e10 : 1
  }
)
// { type: 'LineString', coordinates: [[0,0],[2,0.01],[4,0]] }

// Mutates in place
const geometry = { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0]] }
const result = simplifyGeometry(geometry, { tolerance: 1e-4 })
result === geometry // true

---

simplifyGeoJson

Signature

simplifyGeoJson (geoJson, options)

Description

Simplifies all coordinate sequences of any GeoJSON object using the Visvalingam-Whyatt algorithm. Accepts a plain geometry, a Feature, or a FeatureCollection. Features with a null geometry are skipped silently. The operation is performed in place — the original object is mutated and returned.

Parameters

Name	Type	Required	Description
geoJson	object	yes	Any valid GeoJSON object (geometry, Feature, or FeatureCollection)
options.tolerance	number	no	Minimum triangle area threshold below which a point is removed (default: 0)
options.getWeight	function	no	A function (coord, index) => number that returns a weight multiplied by the triangle area of each point. Defaults to () => 1 (no weighting)

Returns

Type	Description
object	The mutated GeoJSON object

Throws

Throws if geoJson is not a valid GeoJSON object.

Examples

// Plain geometry
simplifyGeoJson(
  { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0.02],[3,0.01],[4,0]] },
  { tolerance: 1e-4 }
)
// { type: 'LineString', coordinates: [[0,0],[4,0]] }

// Feature
simplifyGeoJson(
  {
    type: 'Feature',
    properties: { name: 'Route' },
    geometry: { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0.02],[3,0.01],[4,0]] }
  },
  { tolerance: 1e-4 }
)
// {
//   type: 'Feature',
//   properties: { name: 'Route' },
//   geometry: { type: 'LineString', coordinates: [[0,0],[4,0]] }
// }

// Feature with null geometry — skipped silently
simplifyGeoJson(
  { type: 'Feature', geometry: null, properties: {} },
  { tolerance: 1e-4 }
)
// { type: 'Feature', geometry: null, properties: {} }

// FeatureCollection
simplifyGeoJson(
  {
    type: 'FeatureCollection',
    features: [
      { type: 'Feature', properties: {}, geometry: { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0]] } },
      { type: 'Feature', properties: {}, geometry: { type: 'LineString', coordinates: [[3,0],[4,0.01],[5,0]] } }
    ]
  },
  { tolerance: 1e-4 }
)
// {
//   type: 'FeatureCollection',
//   features: [
//     { type: 'Feature', properties: {}, geometry: { type: 'LineString', coordinates: [[0,0],[2,0]] } },
//     { type: 'Feature', properties: {}, geometry: { type: 'LineString', coordinates: [[3,0],[5,0]] } }
//   ]
// }

// Mutates in place
const geoJson = {
  type: 'Feature',
  geometry: { type: 'LineString', coordinates: [[0,0],[1,0.01],[2,0]] },
  properties: {}
}
const result = simplifyGeoJson(geoJson, { tolerance: 1e-4 })
result === geoJson // true