@turf/helpers

What is @turf/helpers?

The @turf/helpers package is part of the Turf.js library, which is a modular geospatial engine written in JavaScript. It provides functions to create various simple geometrical features such as points, lines, and polygons, and to manipulate these geometries in various ways. This package is particularly useful for developers working with geographic information systems (GIS) and spatial analysis in web applications.

What are @turf/helpers's main functionalities?

Creating Points

This function creates a GeoJSON Point feature using the provided coordinates. It is useful for representing locations on a map.

const point = turf.point([5, 10]);

Creating LineStrings

This function creates a GeoJSON LineString feature from an array of positions. It is useful for mapping routes or paths.

const line = turf.lineString([[5, 10], [20, 40]]);

Creating Polygons

This function creates a GeoJSON Polygon feature from an array of linear rings. It is used to represent areas such as city boundaries or lakes.

const polygon = turf.polygon([[[5, 10], [20, 40], [40, 0], [5, 10]]]);

Other packages similar to @turf/helpers

leaflet

Leaflet is a leading open-source JavaScript library for mobile-friendly interactive maps. While Leaflet itself focuses more on map interactions and overlays, it can be used in conjunction with other tools for creating and manipulating geographic data, similar to @turf/helpers.

openlayers

OpenLayers is another powerful open-source JavaScript library that handles various map-related tasks. It provides more comprehensive features for handling complex spatial operations compared to @turf/helpers, which is more focused on creating and manipulating simple geometrical features.

README

@turf/helpers

feature

Wraps a GeoJSON Geometry in a GeoJSON Feature.

Parameters

• geometry Geometry input geometry
• properties Object properties

Examples

var geometry = {
     "type": "Point",
     "coordinates": [
       67.5,
       32.84267363195431
     ]
   }

var feature = turf.feature(geometry);

//=feature

Returns FeatureCollection a FeatureCollection of input features

point

Takes coordinates and properties (optional) and returns a new Point feature.

Parameters

• coordinates Array<number> longitude, latitude position (each in decimal degrees)
• properties [Object] an Object that is used as the Feature's properties

Examples

var pt1 = turf.point([-75.343, 39.984]);

//=pt1

Returns Feature<Point> a Point feature

polygon

Takes an array of LinearRings and optionally an Object with properties and returns a Polygon feature.

Parameters

• coordinates Array<Array<Array<number>>> an array of LinearRings
• properties [Object] a properties object

Examples

var polygon = turf.polygon([[
 [-2.275543, 53.464547],
 [-2.275543, 53.489271],
 [-2.215118, 53.489271],
 [-2.215118, 53.464547],
 [-2.275543, 53.464547]
]], { name: 'poly1', population: 400});

//=polygon

• Throws Error throw an error if a LinearRing of the polygon has too few positions or if a LinearRing of the Polygon does not have matching Positions at the beginning & end.

Returns Feature<Polygon> a Polygon feature

lineString

Creates a LineString based on a coordinate array. Properties can be added optionally.

Parameters

• coordinates Array<Array<number>> an array of Positions
• properties [Object] an Object of key-value pairs to add as properties

Examples

var linestring1 = turf.lineString([
[-21.964416, 64.148203],
[-21.956176, 64.141316],
[-21.93901, 64.135924],
[-21.927337, 64.136673]
]);
var linestring2 = turf.lineString([
[-21.929054, 64.127985],
[-21.912918, 64.134726],
[-21.916007, 64.141016],
	[-21.930084, 64.14446]
], {name: 'line 1', distance: 145});

//=linestring1

//=linestring2

• Throws Error if no coordinates are passed

Returns Feature<LineString> a LineString feature

featureCollection

Takes one or more Features and creates a FeatureCollection.

Parameters

• features Array<Feature> input features

Examples

var features = [
 turf.point([-75.343, 39.984], {name: 'Location A'}),
 turf.point([-75.833, 39.284], {name: 'Location B'}),
 turf.point([-75.534, 39.123], {name: 'Location C'})
];

var fc = turf.featureCollection(features);

//=fc

Returns FeatureCollection a FeatureCollection of input features

multiLineString

Creates a Feature<MultiLineString> based on a coordinate array. Properties can be added optionally.

Parameters

• coordinates Array<Array<Array<number>>> an array of LineStrings
• properties [Object] an Object of key-value pairs to add as properties

Examples

var multiLine = turf.multiLineString([[[0,0],[10,10]]]);

//=multiLine

• Throws Error if no coordinates are passed

Returns Feature<MultiLineString> a MultiLineString feature

multiPoint

Creates a Feature<MultiPoint> based on a coordinate array. Properties can be added optionally.

Parameters

• coordinates Array<Array<number>> an array of Positions
• properties [Object] an Object of key-value pairs to add as properties

Examples

var multiPt = turf.multiPoint([[0,0],[10,10]]);

//=multiPt

• Throws Error if no coordinates are passed

Returns Feature<MultiPoint> a MultiPoint feature

multiPolygon

Creates a Feature<MultiPolygon> based on a coordinate array. Properties can be added optionally.

Parameters

• coordinates Array<Array<Array<Array<number>>>> an array of Polygons
• properties [Object] an Object of key-value pairs to add as properties

Examples

var multiPoly = turf.multiPolygon([[[[0,0],[0,10],[10,10],[10,0],[0,0]]]);

//=multiPoly

• Throws Error if no coordinates are passed

Returns Feature<MultiPolygon> a multipolygon feature

geometryCollection

Creates a Feature<GeometryCollection> based on a coordinate array. Properties can be added optionally.

Parameters

• geometries Array<{Geometry}> an array of GeoJSON Geometries
• properties [Object] an Object of key-value pairs to add as properties

Examples

var pt = {
    "type": "Point",
      "coordinates": [100, 0]
    };
var line = {
    "type": "LineString",
    "coordinates": [ [101, 0], [102, 1] ]
  };
var collection = turf.geometryCollection([pt, line]);

//=collection

Returns Feature<GeometryCollection> a GeoJSON GeometryCollection Feature

---

This module is part of the Turfjs project, an open source module collection dedicated to geographic algorithms. It is maintained in the Turfjs/turf repository, where you can create PRs and issues.

Installation

Install this module individually:

$ npm install @turf/helpers

Or install the Turf module that includes it as a function:

$ npm install @turf/turf