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Very similar to this tutorial, I would like to create a MapBox map that at a zoomed out level shows regions (labelled Pcode in my data), but once zoomed it switched to a district level (labelled Name). Ideally both these layers would be part of a single geojson shapefile though that can be loaded from an external source (https://raw.githubusercontent.com/Laurent-Smeets-GSS-Account/geojsons/main/geojsons_files/Districts_261_simplified.json). my questions are

  1. how can I format the geojson in such a way that is possible (in R)? (Maybe it is necessary to combine the district polygons into new region polygons and save a seperate geojson file with these regions that gets loaded at another zoom level?)
  2. how do I load the data into Mapbox to make it switch at a certain zoom level?

I am using this example on how to load the code


    mapboxgl.accessToken = 'MY TOKEN';
    // Create a new map.
    const map = new mapboxgl.Map({
        container: 'map',
        // Choose from Mapbox's core styles, or make your own style with Mapbox Studio
        style: 'mapbox://styles/mapbox/streets-v12',
        center: [-100.04, 38.907],
        zoom: 3
    });

    map.on('load', () => {
        // Add a source for the state polygons.
        map.addSource('states', {
            'type': 'geojson',
            'data': 'https://raw.githubusercontent.com/Laurent-Smeets-GSS-Account/geojsons/main/geojsons_files/Districts_261_simplified.json'
        });

        // Add a layer showing the state polygons.
        map.addLayer({
            'id': 'states-layer',
            'type': 'fill',
            'source': 'states',
            'paint': {
                'fill-color': 'rgba(200, 100, 240, 0.4)',
                'fill-outline-color': 'rgba(200, 100, 240, 1)'
            }
        });

        // When a click event occurs on a feature in the states layer,
        // open a popup at the location of the click, with description
        // HTML from the click event's properties.
        map.on('click', 'states-layer', (e) => {
            new mapboxgl.Popup()
                .setLngLat(e.lngLat)
                .setHTML(e.features[0].properties.Name)
                .addTo(map);
        });

        // Change the cursor to a pointer when
        // the mouse is over the states layer.
        map.on('mouseenter', 'states-layer', () => {
            map.getCanvas().style.cursor = 'pointer';
        });

        // Change the cursor back to a pointer
        // when it leaves the states layer.
        map.on('mouseleave', 'states-layer', () => {
            map.getCanvas().style.cursor = '';
        });
    });
L Smeets
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1 Answers1

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  1. You can combine both sets of features into one GeoJSON FeatureCollection, just be sure to add some property that you can filter on, like:
...
{
  type: 'Feature',
  geometry: {...},
  properties: {
    type: 'district'
  }
}
...
  1. When you load the data, add one source, and two layers. Each layer should have a filter attribute so that only the features of a certain type show in that layer. Make sure one has its visibility set to none when the map first loads.
map.addLayer({
  ...,
  layout: {
    visibility: 'none'
  },
  filter: ['==', 'type', 'district']        
});

map.addLayer({
  ...,
  filter: ['==', 'type', 'pcode']        
});

Then you can follow the same example you posted, and toggle the visibility on zoom.

chriswhong
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  • Thanks, but how do I construct the combine in such away in mapshaper or in R? – L Smeets Nov 29 '22 at 17:36
  • I tried this. but it does not work for some reason (see https://stackoverflow.com/questions/74633249/how-to-update-a-choropleth-layer-by-zoom-level-when-using-a-geojson-in-mapbox) – L Smeets Dec 01 '22 at 08:43