geojson2svg

Converts GeoJSON to an SVG string, given the SVG viewport size and map extent. geojson2svg can be used on the client side (in the browser) or server side (with Node.js).

Check world map, SVG scaled map and color coded map examples to demonstrate that its very easy to convert GeoJSON into map.

🛠 Installation
:car: Usage
:popcorn: Basic Example
🔌 API
✈️ Migration from 1.x to 2.x
📌 Important points
📋 Changelog
🪪 License
🔗 Related useful articles

🛠 Installation

• Using in node.js

  npm install geojson2svg

• For including in html page, download the build file ./dist/geojson2svg.min.js

  <script type="text/javascript" src="path/to/geojson2svg.min.js"></script>

  This creates a global variable 'GeoJSON2SVG' as a Class.

• geojson2svg is also available on cdnjs and can be included like:

  <script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/geojson2svg/x.x.x/geojson2svg.min.js"></script>

:car: Usage

• Using with node.js

  With ES6

  import {GeoJSON2SVG} from 'geojson2svg';
  const converter = new GeoJSON2SVG(options);
  const svgStrings = converter.convert(geojson, options);

  With CommonJS

  const {GeoJSON2SVG} = require('geojson2svg');
  const converter = new GeoJSON2SVG(options);
  const svgStrings = converter.convert(geojson, options);

• Usage in browser:

  const converter = new GeoJSON2SVG(options);
  const svgStrings = converter.convert(geojson,options);

:popcorn: Basic Example

const {GeoJSON2SVG} = require('geojson2svg');

const converter = new GeoJSON2SVG({
  mapExtent: {left: -180, bottom: -90, right: 180, top: 90},
  viewportSize: {width: 200, height: 100},
  attributes: ['properties.class' , 'properties.foo'],
  r: 2
});
const geojsonData = {
  type: 'FeatureCollection',
  features: [{
    type: 'Feature',
    id: 'pt-1',
    geometry: {type:'Point',coordinates:[50, 50]},
    properties: {foo: 'val-1', class: 'point-tree'}
  }, {
    type: 'Feature',
    geometry: {
      type: 'LineString',
      coordinates: [[10, 10],[15, 20],[30, 10]]
    },
    properties: {id: 'ln-1', foo: 'val-2', class: 'line-road', bar: 'val'}
  }, {
    type: 'Feature',
    id: 'pg-1',
    geometry: {
      type: 'LineString',
      coordinates: [[30, 10], [40, 40], [20, 40], [10, 20], [30, 10]]
    },
    properties: {id: 'not-used', foo: 'val-3', class: 'polygon-pond'}
  }]
});

const svgStr = converter.convert(geojsonData);
console.log(svgStr);

// output
// [
//   '<path d="M127.77777777777777,22.22222222222222 m-2,0 a2,2 0 1,1 4,0 a2,2 0 1,1 -4,0" class="point-tree" foo="val-1" id="pt-1"/>',
//   '<path d="M105.55555555555556,44.44444444444444 108.33333333333333,38.888888888888886 116.66666666666666,44.44444444444444" class="line-road" foo="val-2" id="ln-1"/>',
//   '<path d="M116.66666666666666,44.44444444444444 122.22222222222221,27.77777777777778 111.11111111111111,27.77777777777778 105.55555555555556,38.888888888888886 116.66666666666666,44.44444444444444" class="polygon-pond" foo="val-3" id="pg-1"/>'
// ]

convert function returns an array of SVG elements' strings.

✈️ Migration from 1.x to 2.x

• Default export as a function is removed. Now geojson2svg exports class GeoJSON2SVG.

  With 1.x

  const geojson2svg = require('geojson2svg');
  const converter = geojson2svg(options);

  Now with 2.x

    // With ES6
    import {GeoJSON2SVG} from 'geojson2svg';
    const converter = new GeoJSON2SVG(options);
    const svgStrings = converter.convert(geojson, options);
  
    // With CommonJS
    const {GeoJSON2SVG} = require('geojson2svg');
    const converter = new GeoJSON2SVG(options);

• Default value of mapExtent in 1.x was Web Mercator projection's full extent. In 2.x if mapExtent is not provided the mapExtentFromGeoJSON is considered to be true, that means the extent of the input data is considered as mapExtent.

• There is only one case (from 1.x to 2.x) for which your existing code would fail, the input GeoJSON data projection system is Web Mercator and you have not specified mapExtent. So to work with 2.x just pass the mapExtent as Web Mercator extent

🔌 API

Initializing the instance

const converter = new GeoJSON2SVG(options);

Here are all options available for initializing the instance.

• viewportSize is object containing width and height in pixels. Default viewportSize value is: {width: 256, height: 256}

• mapExtent: {"left": coordinate, "bottom": coordinate, "right": coordinate, "top": coordinate}. Coordinates should be in same projection as of GeoJSON data. NOTE: If mapExtent is not defined, the parameter mapExtentFromGeojson is considered true.

• mapExtentFromGeojson: boolean, if true mapExtent is calculated from GeoJSON data that is passed in .convert function.

• fitTo: 'width' | 'height' Fit output SVG map to width or height. If nothing is provided, the program tries to fit the data within width or height so that full mapExtent is visible in viewport.

• coordinateCoverter: 'function' to convert input GeoJSON coordinates while converting to SVG. This function should take coordinates of a point [x,y] and returns transformed point [x, y].

• pointAsCircle: true | false, default is false. For point GeoJSON return circle element for option: { "pointAsCircel": true } output SVG string would be:

  '<cirlce cx="30" cy="40" r="1" />'

• r: radius of point SVG element

• attributes: Attributes which are required to attach as SVG attributes from features can be passed here as list of path in feature or json object for static attributes, like shown here

  dynamic {"attributes": ["properties.foo", "properties.bar"]}

  output: [<path foo="fooVal-1" bar="barVal-1" d="M0,0 20,10 106,40"/>]

  or static {"attributes": {"class": "mapstyle"}}

  outut: '<path class="mapstyle" d="M0,0 20,10 106,40"/>'

  or dynamic and static both

  {attributes: [
    {
      property: 'properties.foo',
      type: 'dynamic',
      key: 'id'
    }, {
      property: 'properties.baz',
      type: 'dynamic'
    }, {
      property: 'bar',
      value: 'barStatic',
      type: 'static'
    }]
  })

  output: [ '<path d="M128,128 128.00638801979818,127.99361198020182" id="fooVal-1" baz="bazVal-1" bar="barStatic"/>']

  Note: If a feature does not have value at the mentioned path then the attribute key would not be attached to SVG string and no error would be thrown.

• explode: true | false, default is false. Should multigeojson be exploded to many SVG elements or not.

• precision number, precision of output SVG coordinates. Default is false.

• output: 'svg'|'path' default is 'svg'

  'svg' - SVG element string is returned like '<path d="M0,0 20,10 106,40"/>'

  'path' - path 'd' value is returned 'M0,0 20,10 106,40' a linestring

• callback: function, accept function that will be called on every GeoJSON conversion with output string as one input variable e.g:

  { "callback": function(svgString) {
    // do something with svgString
  }}

  Callback function could be used to render SVG string.

Instance method

.convert(geojson, options)

The options 'attributes', 'r' and 'callback' can also be given in convert function's option. Example:

let svgStrings = convertor.convert(geojson,
  {
    "attributes": ...,
    "r": ...,
    "callback": function
  }
);

📌 Important points

• mapExtent is critical option. Usually your data would would be in WGS84 (World Geodetic System) and unit as degree decimal for latitudes and longitude. Spatial reference system code for this is "EPSG:4326". To show the geographic data on two dimensional plane (paper or HTML page) the coordinates need to be projected. The usual choice is Web Mercator projection ('EPSG:3857') also known as Spherical Mercator. Web Mercator projection is used by many web mapping sites (OpenStreetMap, Google, Bing, and others). Geographic coordinates can be converted to Web Mercator Projection using reproject-spherical-mercator or reproject or proj4js. Check world map example for detail.

• Assigning id to SVG path, there are two ways to achieve this. The first is default, the converter reads it from GeoJSON data attributes feature.properties.id or feature.id. Another way is explicitly specify the id attributes in .convert method, pass id along with attributes like converter.convert(feature, {attributes: {id:'foo-1', class: 'bar'}}). Preference order is: first as id key in attributes then feature.id and last feature.properties.id.

• Converting SVG string to HTML DOM element, the SVG strings returned by convert method can be easily converted to HTML SVG elements. Intentionally I have kept the geojson2svg's output as string to make it more modular. Here is simple way to convert SVG strings to SVG elements with parse-svg or with any other parser. Read more about SVG string conversion to DOM Element here or here. The usage of 'parse-svg' is as follows:

  npm install parse-svg

  or include in your html file

  <script type="text/javascript" src="path/to/parse-svg.min.js"></script>

  Simple way to convert svgStrings to SVG elements

  var parseSVG = require('parse-svg');
  var svgElements = svgStrings.map(parseSVG);

📋 Changelog

Check here

🪪 License

This project is licensed under the terms of the MIT license.

🔗 Related useful articles

• CSS-TRICKS: SVG Properties and CSS
• MDN SVG Tutorial: SVG and CSS
• JENKOV SVG Tutorial: SVG and CSS - Cascading Style Sheets
• Check my blog maps-on-blackboard for more detailed examples using geojson2svg.