SVG 2 GeoJSON

Converts an SVG file with added geo-referencing tags into one or more GeoJSON files.

Installing

npm install svg2geojson

Geo-Referencing Tags

You must place two GeoItems inside a Prognoz MetaInfo element as a direct child of the <svg> element at the root of your document.

<MetaInfo xmlns="http://www.prognoz.ru"><Geo>
  <GeoItem X="-595.30" Y="-142.88" Latitude="37.375593" Longitude="-121.977795"/>
  <GeoItem X="1388.66" Y=" 622.34" Latitude="37.369930" Longitude="-121.959404"/>
</Geo></MetaInfo>

These map opposing X/Y corners in your SVG coordinate space to Longitude/Latitude coordinates on the world. Note that the SVG coordinate space has Y increasing down (toward the south), while Latitude increases upwards (towards the north).

Usage

Running the binary from the command line:

$ npm install -g svg2geojson
$ svg2geojson file.svg          # Writes file.geojson
$ svg2geojson file.svg --layers # Writes file.geojson, file-layer1Name.geojson, …
# See svg2geojson --help for more parameters

Running as a Node.js library:

const { geoFromSVGFile, geoFromSVGXML } = require('svg2geojson.js');

// …reading from file on disk
geoFromSVGFile(
  'my.svg',
  (layers) => {
    layers.forEach((layer) => {
      let json = JSON.stringify(layer.geo); // Turn JS object into JSON string
      console.log(`Layer Named: "${layer.name}"`);
      console.log(json);
    });
  },
  { layers: true, tolerance: 0.5 }
);

// …processing SVG code as a string
const svg = `<svg xmlns="http://www.w3.org/2000/svg"><!-- ... --></svg>`;
geoFromSVGXML(svg, (layer) => {
  let json = JSON.stringify(layer.geo); // Turn JS object into JSON string
  console.log(json);
});

See the output of svg2geojson --help for the options you can pass to the functions, and their default values.

Preparing Paths

SVG allows <path> elements with an arbitrary number of overlapping subpaths, with some of them being 'positive' space and some 'negative' space. In SVG these subpaths may be oriented clockwise or counter-clockwise, and added in any order.

GeoJSON only allows a Polygon to have a single 'positive' subpath (and an arbitrary number of additional 'hole' subpaths). To make it easier for the code to detect which subpath is the 'positive' subpath you must currently:

1. Have only one positive subpath per <path>.
2. Ensure that the positive subpath is the first subpath in a <path>.

TODO (AKA Known Limitations)

• Support modes of projection unmapping
• Support non-rectangular, inverse bilinear unmappings
• Add more command-line options to control JSON formatting.
• Treat <g> as MultiPolygon, GeometryCollection, or MultiLineString as appropriate. Currently items within a group are flattened as individual Feature items in the GeoJSON.
• Treat <path> with multiple positive subpaths as a MultiPolygon. (This requires figuring out which holes apply to which positive subpaths.)