geojson-walk

A tiny library to apply a function to a GeoJSON. In case of a FeatureCollection, the function will also be applied to the single Features.

This can be used to eg. gather statistics about the GeoJSON (spatial extent, attributes, …) or to change / clean it. Have a look at the examples below to get an idea of what is possible.

Installation

npm i @terrestris/geojson-walk

API

This module exposes one function walk:

walk(o, fn, doExpectChange) ⇒ `object`

Walk the GeoJSON and apply the provided function to it or its features (in case of a FeatureCollection). If you expect your function to change the passed GeoJSON Feature Collection, then pass the third parameter as true. In that case the return value of the function determines what ends up in the returned GeoJSON. If you return something truthy, the return value will be used, otherwise the Feature will not be in the returned collection.

Kind: global function Returns: object - The (possibly changed) GeoJSON.

Param	Type	Description
o	`object`	The GeoJSON we will walk. We do not check whether this is actually a fully valid GeoJSON.
fn	`function`	The function we will call. Will receive the GeoJSON or each feature of the collection.
doExpectChange	`boolean`	Whether you expect your function might change the GeoJSON.

Example

Simple usage example:

import walk from '@terrestris/geojson-walk';

const filterForProp = (f) => {
  if (f.properties.humpty === 'dumpty') {
    return f;
  } else {
    return null;
  }
};

const featureCollection = {
  type: 'FeatureCollection',
  features: [
    {
      type: 'Feature',
      properties: {
        humpty: 'dumpty'
      },
      geometry: {
        type: 'Point',
        coordinates: [
          0,
          1
        ]
      }
    },
    {
      type: 'Feature',
      properties: {
        humpty: 'trumpty'
      },
      geometry: {
        type: 'Point',
        coordinates: [
          2,
          3
        ]
      }
    }
  ]
};

const cleanCollection = walk(featureCollection, filterForProp, true);