Leaflet.Deflate

Leaflet.Deflate is a plugin for Leaflet that improves the readability of large-scale web maps. It substitutes polygons and lines with markers when their screen size falls below a defined threshold.

Installation

Using a hosted version

Include the source into the head section of your document.

<script src="https://unpkg.com/Leaflet.Deflate/dist/L.Deflate.js"></script>

Install via NPM

If you use the npm package manager, you can fetch a local copy by running:

npm install Leaflet.Deflate

You will find a copy of the release files in node_modules/Leaflet.Deflate/dist.

API

L.deflate

L.deflate is the main class of Leaflet.Deflate. Use it to create a feature group that deflates all layers added to the group.

Usage example

Initialize L.deflate and add it to your map. Then add layers you want to deflate.

const map = L.map("map");
const features = L.deflate({minSize: 10})
features.addTo(map);

// add layers
const polygon = L.polygon([
    [51.509, -0.08],
    [51.503, -0.06],
    [51.51, -0.047]
])
.addTo(features);

// works with GeoJSONLayer too
L.geoJson(json).addTo(features);

Creation

Options

Examples

Basic

To create a basic deflatable layer, you have to

1. Create an L.deflate feature group and add it to your map.
2. Add features to the L.Deflate feature group.

const map = L.map("map").setView([51.505, -0.09], 12);

const deflate_features = L.deflate({minSize: 20});
deflate_features.addTo(map);

const polygon = L.polygon([
    [51.509, -0.08],
    [51.503, -0.06],
    [51.51, -0.047]
]);
polygon.addTo(deflate_features);

const polyline = L.polyline([
    [51.52, -0.05],
    [51.53, -0.10],
], {color: 'red'});
polyline.addTo(deflate_features);

GeoJSON

GeoJSON layers can be added in the same way:

const map = L.map("map").setView([51.505, -0.09], 12);

const deflate_features = L.deflate({minSize: 20});
deflate_features.addTo(map);

const json = {
    "type": "FeatureCollection",
    "features": [{}]
}

L.geoJson(json, {style: {color: '#0000FF'}}).addTo(deflate_features);

Custom markers

You can change the appearance of markers representing deflated features by providing:

• A marker-options object, or
• A function that returns a marker-options object.

Providing a marker-options object is usually sufficient. You would typically choose to provide a function if you want to base the marker appearance on the feature's properties.

Provide the object or function to the markerOptions property when initializing L.deflate.

Define custom markers using a marker options object

const map = L.map("map").setView([51.550406, -0.140765], 16);

const myIcon = L.icon({
  iconUrl: 'img/marker.png',
  iconSize: [24, 24]
});

const features = L.deflate({minSize: 20, markerOptions: {icon: myIcon}});
features.addTo(map);

Define custom markers using a function

const map = L.map("map").setView([51.550406, -0.140765], 16);

function options(f) {
    // Use custom marker only for buildings
    if (f.feature.properties.type === 'building') {
        return {
            icon: L.icon({
                iconUrl: 'img/marker.png',
                iconSize: [24, 24]
            })
        }
    }

    return {};
}

const features = L.deflate({minSize: 20, markerOptions: options});
features.addTo(map);

CircleMarkers

Alternatively to standard markers, you can use CircleMarker objects to represent deflated features on the map.

To use default circle markers, specify the markerType option.

const map = L.map("map").setView([51.550406, -0.140765], 16);

const features = L.deflate({
    minSize: 20,
    markerType: L.circleMarker
});
features.addTo(map);

Customise CircleMarker

Similar to standard markers, you can customise how circle markers are displayed using the markerOptions property. There are to options to provide the options for circle markers:

• A CircleMarker-options object, or
• A function that returns a CircleMarker-options object.

Define custom circle markers using a CircleMarker options object

const map = L.map("map").setView([51.550406, -0.140765], 16);

const features = L.deflate({
    minSize: 20,
    markerType: L.circleMarker,
    markerOptions: {
        radius: 3,
        color: '#ff0000'
    }
});
features.addTo(map);

Define custom markers using a function

const map = L.map("map").setView([51.550406, -0.140765], 16);

function options(f) {
    // Use custom marker only for buildings
    if (f.feature.properties.type === 'building') {
        return {
            radius: 3,
            color: '#ff0000'
        }
    }

    return {};
}

const features = L.deflate({
    minSize: 20,
    markerType: L.circleMarker,
    markerOptions: options
});
features.addTo(map);

Cluster Markers

Using Leaflet.Markercluster, you can cluster markers. To enable clustered markers on a map:

1. Add the Leaflet.Markercluster libraries to the head section of your document as described in the MarkerCluster documentation.
2. Inject a MarkerClusterGroup instance via the markerLayer option when initializing L.deflate.

const map = L.map("map").setView([51.505, -0.09], 12);

const markerLayer = L.markerClusterGroup();
const deflate_features = L.deflate({minSize: 20, markerLayer: markerLayer});
deflate_features.addTo(map);

const polygon = L.polygon([
    [51.509, -0.08],
    [51.503, -0.06],
    [51.51, -0.047]
]);
polygon.addTo(deflate_features)

const polyline = L.polyline([
    [51.52, -0.05],
    [51.53, -0.10],
], {color: 'red'});
polyline.addTo(deflate_features)

Leaflet.Draw

Leaflet.Draw is a plugin that adds support for drawing and editing vector features on Leaflet maps. Leaflet.Deflate integrates with Leaflet.Draw.

Initialize the Leaflet.draw control. Use the L.deflate instance to draw and edit features and add it the map.

To ensure that newly added or edited features are deflated at the correct zoom level and show the marker at the correct location, you need to call prepLayer with the edited layer on every change. In the example below, we call prepLayer inside the handler function for the L.Draw.Event.EDITED event.

const map = L.map("map").setView([51.505, -0.09], 12);

const deflate_features = L.deflate({minSize: 20, markerCluster: true});
deflate_features.addTo(map);

const drawControl = new L.Control.Draw({
    edit: {
        featureGroup: deflate_features
    }
});
map.addControl(drawControl);

map.on(L.Draw.Event.CREATED, function (event) {
    const layer = event.layer;
    deflate_features.addLayer(layer);
});

map.on(L.Draw.Event.EDITED, function(event) {
    const editedLayers = event.layers;
    editedLayers.eachLayer(function(l) {
        deflate_features.prepLayer(l);
    });
});

Developing

You'll need to install the dev dependencies to test and write the distribution file.

npm install

To run tests:

npm test

To run eslint on source and test code:

npm run lint

To write a minified JS into dist:

npm run dist

Releasing

npm version is set up to take it all the way to npm.

Authors

• Lindsey Jacks
• Loic Lacroix
• Oliver Roick

License

Apache 2.0