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geojson-multiply: a simple package to pack single tyle geojson features

Posted on Edited on In Disqus:

Some PostGIS functions only accept multi type geometry, so I write a simple geojson utility package to help me aggregate geojson features.

The basic purpose of geojson-multiply is to generate a MutliPoint/MultiLineString/MultiPolygon geojson feature from many Point/LineString/Polygon geojson features. So this package provides a function

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multiply(geojsons[, options])

Where the geojsons could be a geojson feature, an array of geojson features, or a geojson feature collection

Not just the coordinates, the multiply() also supports the aggregation of properties. Its options parameter accepts two input:

  • properties - the default properties of result geojson

  • onEachFeature - a function to aggregate properties. It has four parameters:

    • properties - the result geojson’s properties

    • featureProp - input feature geojson’s properties

    • index - input feature geojson’s index in the array

    • geojsons - geojson array.

It takes the form of Array.reduce() and make the aggregation pretty straightforward:

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var multiply = require('geojson-multiply');

var geojsonA = {
  type: 'Feature',
  geometry: { type: 'Point', coordinates: [12, 43] },
  properties: { count: 5 }
};

var geojsonB = {
  type: 'Feature',
  geometry: { type: 'Point', coordinates: [13, 34] },
  properties: { count: 5 }
};

var onEachFeature = function(properties, featureProp) {
  properties.count += featureProp.count;
  return properties;
};

var result = multiply([geojsonA, geojsonB], {
  properties: { count: 0 },
  onEachFeature: onEachFeature
});

/**
The reuslt geojson should be
{
  type: 'Feature'
  geometry: {
    type: 'MultiPoint',
    coordinates: [[12, 43], [14, 34]]
  },
  properties: {
    count: 10
  }
}
*/

This package has been published at npm. If you think it’s helpful, just install and try!

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npm install geojson-multiply --save