@turf/meta

What is @turf/meta?

@turf/meta is a module of the Turf.js library that provides utility functions for working with GeoJSON data. It allows you to iterate over various GeoJSON objects, extract specific properties, and manipulate geometries.

What are @turf/meta's main functionalities?

coordEach

The `coordEach` function iterates over each coordinate in any GeoJSON object, allowing you to perform operations on each coordinate.

const turf = require('@turf/meta');
const point = { "type": "Feature", "geometry": { "type": "Point", "coordinates": [110, 50] } };
turf.coordEach(point, function (coord) {
  console.log(coord);
});

propEach

The `propEach` function iterates over properties in any GeoJSON Feature or FeatureCollection, allowing you to access and manipulate properties.

const turf = require('@turf/meta');
const featureCollection = { "type": "FeatureCollection", "features": [ { "type": "Feature", "properties": { "name": "A" }, "geometry": { "type": "Point", "coordinates": [110, 50] } } ] };
turf.propEach(featureCollection, function (properties, featureIndex) {
  console.log(properties);
});

geomEach

The `geomEach` function iterates over each geometry in any GeoJSON object, allowing you to perform operations on each geometry.

const turf = require('@turf/meta');
const featureCollection = { "type": "FeatureCollection", "features": [ { "type": "Feature", "geometry": { "type": "Point", "coordinates": [110, 50] } } ] };
turf.geomEach(featureCollection, function (geometry, featureIndex) {
  console.log(geometry);
});

Other packages similar to @turf/meta

geojson-utils

The `geojson-utils` package provides utility functions for manipulating and analyzing GeoJSON data. It offers similar functionalities to @turf/meta, such as iterating over coordinates and geometries, but it also includes additional features like distance calculations and point-in-polygon tests.

geolib

The `geolib` package is a library for geospatial calculations. While it does not focus specifically on GeoJSON, it provides a wide range of geospatial utilities, including distance calculations, bounding box operations, and coordinate transformations. It can be used in conjunction with GeoJSON data for various geospatial tasks.

geojson-extent

The `geojson-extent` package is designed to calculate the bounding box of GeoJSON objects. While it does not offer the same breadth of functionality as @turf/meta, it is useful for specific tasks related to determining the spatial extent of GeoJSON data.

README

@turf/meta

coordEachCallback

Callback for coordEach

Parameters

• currentCoord Array<number> The current coordinate being processed.
• coordIndex number The current index of the coordinate being processed. Starts at index 0.
• featureIndex number The current index of the feature being processed.
• featureSubIndex number The current subIndex of the feature being processed.
• geojson
• callback
• excludeWrapCoord

coordEach

Iterate over coordinates in any GeoJSON object, similar to Array.forEach()

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object
• callback Function a method that takes (currentCoord, coordIndex, featureIndex, featureSubIndex)
• excludeWrapCoord [boolean] whether or not to include the final coordinate of LinearRings that wraps the ring in its iteration. (optional, default false)

Examples

var features = turf.featureCollection([
  turf.point([26, 37], {"foo": "bar"}),
  turf.point([36, 53], {"hello": "world"})
]);

turf.coordEach(features, function (currentCoord, coordIndex, featureIndex, featureSubIndex) {
  //=currentCoord
  //=coordIndex
  //=featureIndex
  //=featureSubIndex
});

coordReduce

Reduce coordinates in any GeoJSON object, similar to Array.reduce()

Parameters

• geojson (FeatureCollection | Geometry | Feature) any GeoJSON object
• callback Function a method that takes (previousValue, currentCoord, coordIndex)
• initialValue [Any] Value to use as the first argument to the first call of the callback.
• excludeWrapCoord [boolean] whether or not to include the final coordinate of LinearRings that wraps the ring in its iteration. (optional, default false)

Examples

var features = turf.featureCollection([
  turf.point([26, 37], {"foo": "bar"}),
  turf.point([36, 53], {"hello": "world"})
]);

turf.coordReduce(features, function (previousValue, currentCoord, coordIndex, featureIndex, featureSubIndex) {
  //=previousValue
  //=currentCoord
  //=coordIndex
  //=featureIndex
  //=featureSubIndex
  return currentCoord;
});

Returns Any The value that results from the reduction.

coordReduceCallback

Callback for coordReduce

The first time the callback function is called, the values provided as arguments depend on whether the reduce method has an initialValue argument.

If an initialValue is provided to the reduce method:

• The previousValue argument is initialValue.
• The currentValue argument is the value of the first element present in the array.

If an initialValue is not provided:

• The previousValue argument is the value of the first element present in the array.
• The currentValue argument is the value of the second element present in the array.

Parameters

• previousValue Any The accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied.
• currentCoord Array<number> The current coordinate being processed.
• coordIndex number The current index of the coordinate being processed. Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• featureIndex number The current index of the feature being processed.
• featureSubIndex number The current subIndex of the feature being processed.
• geojson
• callback
• initialValue
• excludeWrapCoord

propEach

Iterate over properties in any GeoJSON object, similar to Array.forEach()

Parameters

• geojson (FeatureCollection | Feature) any GeoJSON object
• callback Function a method that takes (currentProperties, featureIndex)

Examples

var features = turf.featureCollection([
    turf.point([26, 37], {foo: 'bar'}),
    turf.point([36, 53], {hello: 'world'})
]);

turf.propEach(features, function (currentProperties, featureIndex) {
  //=currentProperties
  //=featureIndex
});

propEachCallback

Callback for propEach

Parameters

• currentProperties Object The current properties being processed.
• featureIndex number The index of the current element being processed in the array.Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• geojson
• callback

propReduce

Reduce properties in any GeoJSON object into a single value, similar to how Array.reduce works. However, in this case we lazily run the reduction, so an array of all properties is unnecessary.

Parameters

• geojson (FeatureCollection | Feature) any GeoJSON object
• callback Function a method that takes (previousValue, currentProperties, featureIndex)
• initialValue [Any] Value to use as the first argument to the first call of the callback.

Examples

var features = turf.featureCollection([
    turf.point([26, 37], {foo: 'bar'}),
    turf.point([36, 53], {hello: 'world'})
]);

turf.propReduce(features, function (previousValue, currentProperties, featureIndex) {
  //=previousValue
  //=currentProperties
  //=featureIndex
  return currentProperties
});

Returns Any The value that results from the reduction.

propReduceCallback

Callback for propReduce

The first time the callback function is called, the values provided as arguments depend on whether the reduce method has an initialValue argument.

If an initialValue is provided to the reduce method:

• The previousValue argument is initialValue.
• The currentValue argument is the value of the first element present in the array.

If an initialValue is not provided:

• The previousValue argument is the value of the first element present in the array.
• The currentValue argument is the value of the second element present in the array.

Parameters

• previousValue Any The accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied.
• currentProperties Any The current properties being processed.
• featureIndex number The index of the current element being processed in the array.Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• geojson
• callback
• initialValue

featureEach

Iterate over features in any GeoJSON object, similar to Array.forEach.

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object
• callback Function a method that takes (currentFeature, featureIndex)

Examples

var features = turf.featureCollection([
  turf.point([26, 37], {foo: 'bar'}),
  turf.point([36, 53], {hello: 'world'})
]);

turf.featureEach(features, function (currentFeature, featureIndex) {
  //=currentFeature
  //=featureIndex
});

featureEachCallback

Callback for featureEach

Parameters

• currentFeature Feature<any> The current feature being processed.
• featureIndex number The index of the current element being processed in the array.Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• geojson
• callback

featureReduceCallback

Callback for featureReduce

The first time the callback function is called, the values provided as arguments depend on whether the reduce method has an initialValue argument.

If an initialValue is provided to the reduce method:

• The previousValue argument is initialValue.
• The currentValue argument is the value of the first element present in the array.

If an initialValue is not provided:

• The previousValue argument is the value of the first element present in the array.
• The currentValue argument is the value of the second element present in the array.

Parameters

• previousValue Any The accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied.
• currentFeature Feature The current Feature being processed.
• featureIndex number The index of the current element being processed in the array.Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• geojson
• callback
• initialValue

featureReduce

Reduce features in any GeoJSON object, similar to Array.reduce().

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object
• callback Function a method that takes (previousValue, currentFeature, featureIndex)
• initialValue [Any] Value to use as the first argument to the first call of the callback.

Examples

var features = turf.featureCollection([
  turf.point([26, 37], {"foo": "bar"}),
  turf.point([36, 53], {"hello": "world"})
]);

turf.featureReduce(features, function (previousValue, currentFeature, featureIndex) {
  //=previousValue
  //=currentFeature
  //=featureIndex
  return currentFeature
});

Returns Any The value that results from the reduction.

coordAll

Get all coordinates from any GeoJSON object.

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object

Examples

var features = turf.featureCollection([
  turf.point([26, 37], {foo: 'bar'}),
  turf.point([36, 53], {hello: 'world'})
]);

var coords = turf.coordAll(features);
//= [[26, 37], [36, 53]]

Returns Array<Array<number>> coordinate position array

geomEachCallback

Callback for geomEach

Parameters

• currentGeometry Geometry The current geometry being processed.
• currentIndex number The index of the current element being processed in the array. Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• currentProperties number The current feature properties being processed.
• geojson
• callback

geomEach

Iterate over each geometry in any GeoJSON object, similar to Array.forEach()

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object
• callback Function a method that takes (currentGeometry, featureIndex, currentProperties)

Examples

var features = turf.featureCollection([
    turf.point([26, 37], {foo: 'bar'}),
    turf.point([36, 53], {hello: 'world'})
]);

turf.geomEach(features, function (currentGeometry, featureIndex, currentProperties) {
  //=currentGeometry
  //=featureIndex
  //=currentProperties
});

geomReduceCallback

Callback for geomReduce

The first time the callback function is called, the values provided as arguments depend on whether the reduce method has an initialValue argument.

If an initialValue is provided to the reduce method:

• The previousValue argument is initialValue.
• The currentValue argument is the value of the first element present in the array.

If an initialValue is not provided:

• The previousValue argument is the value of the first element present in the array.
• The currentValue argument is the value of the second element present in the array.

Parameters

• previousValue Any The accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied.
• currentGeometry Geometry The current Feature being processed.
• currentIndex number The index of the current element being processed in the array.Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• currentProperties Object The current feature properties being processed.
• geojson
• callback
• initialValue

geomReduce

Reduce geometry in any GeoJSON object, similar to Array.reduce().

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object
• callback Function a method that takes (previousValue, currentGeometry, featureIndex, currentProperties)
• initialValue [Any] Value to use as the first argument to the first call of the callback.

Examples

var features = turf.featureCollection([
    turf.point([26, 37], {foo: 'bar'}),
    turf.point([36, 53], {hello: 'world'})
]);

turf.geomReduce(features, function (previousValue, currentGeometry, featureIndex, currentProperties) {
  //=previousValue
  //=currentGeometry
  //=featureIndex
  //=currentProperties
  return currentGeometry
});

Returns Any The value that results from the reduction.

flattenEachCallback

Callback for flattenEach

Parameters

• currentFeature Feature The current flattened feature being processed.
• featureIndex number The index of the current element being processed in the array. Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• featureSubIndex number The subindex of the current element being processed in the array. Starts at index 0 and increases if the flattened feature was a multi-geometry.
• geojson
• callback

flattenEach

Iterate over flattened features in any GeoJSON object, similar to Array.forEach.

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object
• callback Function a method that takes (currentFeature, featureIndex, featureSubIndex)

Examples

var features = turf.featureCollection([
    turf.point([26, 37], {foo: 'bar'}),
    turf.multiPoint([[40, 30], [36, 53]], {hello: 'world'})
]);

turf.flattenEach(features, function (currentFeature, featureIndex, featureSubIndex) {
  //=currentFeature
  //=featureIndex
  //=featureSubIndex
});

flattenReduceCallback

Callback for flattenReduce

The first time the callback function is called, the values provided as arguments depend on whether the reduce method has an initialValue argument.

If an initialValue is provided to the reduce method:

• The previousValue argument is initialValue.
• The currentValue argument is the value of the first element present in the array.

If an initialValue is not provided:

• The previousValue argument is the value of the first element present in the array.
• The currentValue argument is the value of the second element present in the array.

Parameters

• previousValue Any The accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied.
• currentFeature Feature The current Feature being processed.
• featureIndex number The index of the current element being processed in the array.Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• featureSubIndex number The subindex of the current element being processed in the array. Starts at index 0 and increases if the flattened feature was a multi-geometry.
• geojson
• callback
• initialValue

flattenReduce

Reduce flattened features in any GeoJSON object, similar to Array.reduce().

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON object
• callback Function a method that takes (previousValue, currentFeature, featureIndex, featureSubIndex)
• initialValue [Any] Value to use as the first argument to the first call of the callback.

Examples

var features = turf.featureCollection([
    turf.point([26, 37], {foo: 'bar'}),
    turf.multiPoint([[40, 30], [36, 53]], {hello: 'world'})
]);

turf.flattenReduce(features, function (previousValue, currentFeature, featureIndex, featureSubIndex) {
  //=previousValue
  //=currentFeature
  //=featureIndex
  //=featureSubIndex
  return currentFeature
});

Returns Any The value that results from the reduction.

segmentEachCallback

Callback for segmentEach

Parameters

• currentSegment Feature<LineString> The current segment being processed.
• segmentIndex number The segmentIndex currently being processed, starts at index 0.
• featureIndex number The featureIndex currently being processed, starts at index 0.
• featureSubIndex number The featureSubIndex currently being processed, starts at index 0.
• geojson
• callback

Returns void

segmentEach

Iterate over 2-vertex line segment in any GeoJSON object, similar to Array.forEach() (Multi)Point geometries do not contain segments therefore they are ignored during this operation.

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON
• callback Function a method that takes (currentSegment, featureIndex, featureSubIndex)

Examples

var polygon = turf.polygon([[[-50, 5], [-40, -10], [-50, -10], [-40, 5], [-50, 5]]]);

// Iterate over GeoJSON by 2-vertex segments
turf.segmentEach(polygon, function (currentSegment, featureIndex, featureSubIndex) {
  //= currentSegment
  //= segmentIndex
  //= featureIndex
  //= featureSubIndex
});

// Calculate the total number of segments
var total = 0;
turf.segmentEach(polygon, function () {
    total++;
});

Returns void

segmentReduceCallback

Callback for segmentReduce

The first time the callback function is called, the values provided as arguments depend on whether the reduce method has an initialValue argument.

If an initialValue is provided to the reduce method:

• The previousValue argument is initialValue.
• The currentValue argument is the value of the first element present in the array.

If an initialValue is not provided:

• The previousValue argument is the value of the first element present in the array.
• The currentValue argument is the value of the second element present in the array.

Parameters

• previousValue [Any] The accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied.
• currentSegment [Feature<LineString>] The current segment being processed.
• segmentIndex number The segmentIndex currently being processed, starts at index 0.
• featureIndex number The featureIndex currently being processed, starts at index 0.
• featureSubIndex number The featureSubIndex currently being processed, starts at index 0.
• geojson
• callback
• initialValue

segmentReduce

Reduce 2-vertex line segment in any GeoJSON object, similar to Array.reduce() (Multi)Point geometries do not contain segments therefore they are ignored during this operation.

Parameters

• geojson (FeatureCollection | Feature | Geometry) any GeoJSON
• callback Function a method that takes (previousValue, currentSegment, currentIndex)
• initialValue [Any] Value to use as the first argument to the first call of the callback.

Examples

var polygon = turf.polygon([[[-50, 5], [-40, -10], [-50, -10], [-40, 5], [-50, 5]]]);

// Iterate over GeoJSON by 2-vertex segments
turf.segmentReduce(polygon, function (previousSegment, currentSegment, segmentIndex, featureIndex, featureSubIndex) {
  //= previousSegment
  //= currentSegment
  //= segmentInex
  //= featureIndex
  //= featureSubIndex
  return currentSegment
});

// Calculate the total number of segments
var initialValue = 0
var total = turf.segmentReduce(polygon, function (previousValue) {
    previousValue++;
    return previousValue;
}, initialValue);

Returns void

lineEachCallback

Callback for lineEach

Parameters

• currentLine Feature<LineString> The current LineString|LinearRing being processed.
• lineIndex number The index of the current element being processed in the array, starts at index 0.
• lineSubIndex number The sub-index of the current line being processed at index 0
• geojson
• callback

lineEach

Iterate over line or ring coordinates in LineString, Polygon, MultiLineString, MultiPolygon Features or Geometries, similar to Array.forEach.

Parameters

• geojson (Geometry | Feature<(LineString | Polygon | MultiLineString | MultiPolygon)>) object
• callback Function a method that takes (currentLine, lineIndex, lineSubIndex)

Examples

var mtLn = turf.multiLineString([
  turf.lineString([[26, 37], [35, 45]]),
  turf.lineString([[36, 53], [38, 50], [41, 55]])
]);

turf.lineEach(mtLn, function (currentLine, lineIndex) {
  //=currentLine
  //=lineIndex
});

lineReduceCallback

Callback for lineReduce

The first time the callback function is called, the values provided as arguments depend on whether the reduce method has an initialValue argument.

If an initialValue is provided to the reduce method:

• The previousValue argument is initialValue.
• The currentValue argument is the value of the first element present in the array.

If an initialValue is not provided:

• The previousValue argument is the value of the first element present in the array.
• The currentValue argument is the value of the second element present in the array.

Parameters

• previousValue Any The accumulated value previously returned in the last invocation of the callback, or initialValue, if supplied.
• currentLine Feature<LineString> The current LineString|LinearRing being processed.
• lineIndex number The index of the current element being processed in the array. Starts at index 0, if an initialValue is provided, and at index 1 otherwise.
• lineSubIndex number The sub-index of the current line being processed at index 0
• geojson
• callback
• initialValue

lineReduce

Reduce features in any GeoJSON object, similar to Array.reduce().

Parameters

• geojson (Geometry | Feature<(LineString | Polygon | MultiLineString | MultiPolygon)>) object
• callback Function a method that takes (previousValue, currentFeature, featureIndex)
• initialValue [Any] Value to use as the first argument to the first call of the callback.

Examples

var mtp = turf.multiPolygon([
  turf.polygon([[[12,48],[2,41],[24,38],[12,48]], [[9,44],[13,41],[13,45],[9,44]]]),
  turf.polygon([[[5, 5], [0, 0], [2, 2], [4, 4], [5, 5]]])
]);

turf.lineReduce(mtp, function (previousValue, currentLine, lineIndex, lineSubIndex) {
  //=previousValue
  //=currentLine
  //=lineIndex
  //=lineSubIndex
  return currentLine
}, 2);

Returns Any The value that results from the reduction.

---

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/meta

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

$ npm install @turf/turf