mapboxgl-legend

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mapboxgl-legend

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Add a legend to a mapbox-gl map by parsing layer layout & paint expressions.

// repository documentation

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# mapboxgl-legend

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Add a legend to a mapbox-gl map by parsing layer layout & paint expressions.

![image](https://user-images.githubusercontent.com/12972543/116700430-0d338b80-a9c7-11eb-913f-70c884589dc0.png)

Properties currently supported:

- `*-color`
- `*-radius`
- `*-image`
- `*-pattern`

Expressions currently supported:

- `case`
- `match`
- `interpolate`
- `step`
- literals

The legend works seamlessly with [MapLibre](https://maplibre.org/) as well.

## Get started

Install npm package

```bash
npm install mapboxgl-legend
```

Add legend control to map

```javascript
import LegendControl from 'mapboxgl-legend';
import 'mapboxgl-legend/dist/style.css';

const legend = new LegendControl();
map.addControl(legend, 'bottom-left');
```

Add layers as usual, and the legend will be autogenerated

```javascript
map.addLayer({
  id: 'density',
  type: 'circle',
  source: 'demographic',
  paint: {
    'circle-radius': [
      'interpolate', ['linear'],
      ['to-number', ['get', 'density']],
      100, 10,
      200, 17,
      500, 30,
      1000, 50,
      2000, 75
    ],
    'circle-color': [
      'match',
      ['get', 'ethnicity'],
      'White', '#f1e8c8',
      'Black', '#443722',
      'Hispanic', '#aa9761',
      'Asian', '#e8e59d',
      /* other */ '#ccc'
    ]
  },
});
```

## Options

A few options can be passed on legend initialization.

| option | type | default | description |
| --- | --- | --- | --- |
| minimized | Boolean, undefined | `undefined` | If set, a button toggles layer visibility. Initial value is set as this attribute |
| collapsed | Boolean | `false` | Set legend panels collapsed on load |
| toggler | Boolean, string[] | `false` | Add button to show and hide layers. Provide an array of layer ids to toggle them with this button |
| highlight | Boolean | `false` | Add interactivity to legend items |
| layers | Array[string, RegExp], Object | `undefined` | List of layers to be added. If undefined all layers will be added |
| onToggle | Function | `undefined` | Set a callback function to a layer visibility change. Function receives as parameters the `layerId` that changed and its visibility (boolean) |

The layers option is an array of the layers' ids, or strings casted as regex that match the layers' ids. It can also be an object with keys being the layers' ids and values being an array of visible attributes, or `true` if all visible. For a fine grained control over layers, this object can also contain the same options `collapsed`, `toggler`, `attributes` and `onToggle`.

```javascript
const legend = new LegendControl({
  // Show all properties in selected layers
  layers: ['population', 'areas', /sw-\d/],
  layers: {
    // Show all properties in this layer
    areas: true,
    // Show only selected properties in this layer
    population: ['circle-radius'], 
    // Fine grained options per layer
    pois: {
      collapsed: true,
      toggler: false,
      highlight: true,
      attributes: ['circle-radius'],
    }
  },
})
```

There are also a few options that be defined as a per-layer basis using the style `metadata` object.

| option | type | description |
| --- | --- | --- |
| name | String | Set the panel title name |
| unit | String | Add a unit to all labels |
| labels | Object | Map a value to a text that replaces it as a label |
| extraLegendClasses | String[] | Classes to add to the layer's legend pane |

Metadata provides an extra layer of control by hiding items that have a label set to `false`, except on step expressions.

```javascript
map.addLayer({
  id: 'density',
  type: 'circle',
  source: 'demographic',
  paint: { /* ... */ },
  metadata: {
    name: 'Population Density',
    unit: 'k/km²',
    labels: {
      10: 'Custom label for value 10',
      other: '< 1k/km²',
      an_item_to_hide: false,
    }
  }
});
```

For pairs labels, such as in `step` expressions, it is possible to labelize by using the serialized array of steps as a key

```javascript
matadata: {
  labels: {
    '0,10': 'Group A',
    '10,20': 'Group B',
  },
}
```

## Handle layers

Layers can be added or removed from legend at any moment by using `legend.addLayers()` with same format as `layers` option and `legend.removeLayers([layerIds])`.

## Styles

Legend defaults to a simple design inspired by standard mapbox-gl controls, but can be tunned by changing CSS variables. Check default values in `/src/styles/_variables.scss`

## Development

Create a `.env` file and set your Mapbox token as `VITE_MAPBOX_TOKEN`.

Run the development server with the command

```bash
npm run dev
```

## Contribute

Whether you're fixing a bug, implementing a new feature, or improving the documentation, your contribution is greatly appreciated.

Start by forking the repository on GitHub, create a new branch and finally submit a Pull Request with your changes. Provide a detailed description of your changes, including any relevant context or references to issues.

By contributing to this project, you agree that your contributions will be licensed under the ISC License.

mapboxgl-legend

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