GeoJSON-js

Use GeoJSON data as a JavaScript Object, including handy object methods.

GeoJSON is a great format for sharing mapping data across different systems and programming languages, especially JavaScript. But on its own, GeoJSON is just a block of data. This GeoJSON Object adds handy reference and utility functions to the data, without changing how you would access the data were it an ordinary JavaScript Object.

A Couple Quick Examples

var example1 = {
  "type": "Feature",
  "geometry": {
    "type": "Polygon",
    "coordinates":[[[20,0],[30,0],[30,10],[20,10],[20,0]]]
  }
}

var myFeature = new GeoJSON.Feature( example1 );

console.log( myFeature.bbox ); //  [20,0,30,10]


var example2 = {
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates":[50,10]
      },
      "properties": {
        "id": 1,
        "label": "First Base"
      }
    },
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates":[40,50]
      },
      "properties": {
        "id": 2,
        "label": "Second Base"
      }
    },
  ]
}

var myBases = new GeoJSON.FeatureCollection( example2 );

console.log( myBases.getFeatureByPropertyValue( "id", 2 ).properties.label ); //  "Second Base"
console.log( myBases.bbox ); //  [40,10,50,50]
myBases.addFeature({
  "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates":[0,40]
  },
  "properties": {
    "id": 3,
    "label": "Third Base"
  }
});
console.log( myBases.bbox ); // [0,10,50,50]

Installation

1. Download or clone this repo.
2. Include the GeoJSON.js script in your web app.

<script src="GeoJSON.js"></script>

Reference

There are currently four object classes at your disposal in this script, each starts with the standard GeoJSON data format, then adds a few convenience methods.

• FeatureCollection
• Feature
• Geometry
• BBox

Methods Common to All GeoJSON-js Classes

Construction:

All class object constructors in GeoJSON-js expect input in the the standard GeoJSON format. See RFC7946 for details.

var fc = new GeoJSON.FeatureCollection( featureCollectionData );
var f = new GeoJSON.Feature( featureData );
var g = new GeoJSON.Geometry( featureGeometryData );

Getting the Bounding-Box

For all classes, the bbox property is automatically calculated when accessed.

var bbox = g.bbox;
var southernmostLatitude = f.bbox[0];

Converting to JSON string:

Class methods and housekeeping properties are automatically stripped out by the toJSON() method and when using JSON.stringify( myObj ).

var jsonString = JSON.stringify( myFeatureClassObject );
var plainObject = myFeatureClassObject.toJSON();

FeatureCollection

Adding one feature:

fc.addFeature( featureData );
// or
fc.features.push( new GeoJSON.Feature( featureData );

Adding multiple features:

fc.addFeatures( arrayOfFeaturesData );

Getting a specific feature by the feature's property value:

var featureClassObject = fc.getFeatureByPropertyValue( propertyKey, desiredValue );

Getting the Bounding-Box

For the FeatureCollection class, the bbox is updated when new features are added with the addFeature and addFeatures methods.

Feature

There are currently no helper methods unique to the Feature class, but it still has the same convenience bbox property and toJSON method.

Geometry

The Geometry class is primarily intended for internal use, and is automatically used within any new Feature Class objects, but you're free to use it if you like.

The Geometry class does the work of verifying incoming data is a supported GeoJSON type and that all lineStrings are "closed", and does the bounding-box calculations. If an invalid 'type' is given, Geometry will throw an "Unsupported geometry type" error. If the first and last points are not the same, it adds a copy of the first point to the end.

Bbox

Like the Geometry class, the Bbox class is mostly intended for internal use, but if all you need is to do some bounding-box calculations, the Bbox class does not depend on any other GeoJSON-js classes.

Construction:

The BBox class expects an array of four or six numbers specifying the minimum and maximum extents of a feature's geometry.

• 2-dimensional: [ minX, minY, maxX, maxY ]
• 3-dimensional: [ minX, minY, minZ, maxX, maxY, maxZ ]

var bboxObject = new GeoJSON.Bbox( bboxArray );

Expanding to Include More Points

The expand method accepts any standard GeoJSON-format coordinates array, from "Point" to "MultiPolygon" and anywhere between.

bboxObject.expand( feature.geometry.coordinates );

Merging Two Bbox Class Objects

The merge method expands a Bbox to include the extent of another Bbox.

bboxObject.merge( otherBboxObject );

Getting Back the Bbox Array

var bboxArray = bboxObject.toJSON();