Leaflet.snogylop

Leaflet.snogylop is a Leaflet plugin that inverts polygons.

Why? you ask. Sometimes you want to highlight a region of a map by de-emphasizing the rest of the map. Using this plugin you can set a relatively high opacity in order to de-emphasize everything outside of a polygon or multipolygon.

Demos

An inverted polygon.

An inverted multipolygon.

Custom worldLatLngs, eg for polygons near the antimeridian.

Usage

Include leaflet.snogylop.js on your page, set the options on your GeoJSON layer as specified below.

Leaflet.snogylop is tested on Leaflet version 0.7 and 1.x with L.GeoJSON layers. It may work with older Leaflets and should work with other layers. Pull requests in this direction are welcome.

AMD compatible.

Available through bower: bower install --save leaflet.snogylop

Options

Define the following option in the vector options when creating a layer (eg, an L.GeoJSON):

• invert: (boolean) True to invert. False by default.
• worldLatLngs: (coordinate array) Optional, the coordinates of the outer ring of the inverted polygon that will be created.

Examples

Create a GeoJSON layer, set invert to true:

L.geoJson(data, {
    invert: true
}).addTo(map);

The default worldLatLngs can be overriden by using the worldLatLngs option:

L.geoJson(data, {
    invert: true,
    worldLatLngs: [
        L.latLng([90, 360]),
        L.latLng([90, -180]),
        L.latLng([-90, -180]),
        L.latLng([-90, 360])
    ]
}).addTo(map);

FAQs

Is there any way to avoid the delay in drawing the polygon when panning and zooming?

Yes, with Leaflet 1.* you can use the renderer option as described in this issue to add padding around the polygon. For example:

L.geoJson(data, {
    invert: true,
    renderer: L.svg({ padding: 1 })
}).addTo(map);

License

Leaflet.snogylop is free software, and may be redistributed under the MIT License.