Basic bubblemap with leaflet.js and d3.js

Steps:

First of all, you need to know how to plot a basic background map with leaflet.

Then we just add circles for each data points as we would do for a scatter plot or a bubble plot.

The only trick is that latitude and longitude coordinates must be converted to pixels. This is done thanks to the latLngToLayerPoint leaflet function.

<!DOCTYPE html>
<meta charset="utf-8">

<!-- Load d3.js and the geo projection plugin -->
<script src="https://d3js.org/d3.v4.js"></script>
<script src="https://d3js.org/d3-geo-projection.v2.min.js"></script>

<!-- Load Leaflet -->
<link rel="stylesheet" href="https://unpkg.com/leaflet@1.3.4/dist/leaflet.css" integrity="sha512-puBpdR0798OZvTTbP4A8Ix/l+A4dHDD0DGqYW6RQ+9jxkRFclaxxQb/SJAWZfWAkuyeQUytO7+7N4QKrDh+drA==" crossorigin=""/>
<script src="https://unpkg.com/leaflet@1.3.4/dist/leaflet.js" integrity="sha512-nMMmRyTVoLYqjP9hrbed9S+FzjZHW5gY1TWCHA5ckwXZBadntCNs8kEqAWdrb9O7rxbCaA4lKTIWjDXZxflOcA==" crossorigin=""></script>

<!-- Create an element where the map will take place -->
<div id="mapid"></div>

<style>
#mapid { height: 400px; }
</style>

<!DOCTYPE html>
<meta charset="utf-8">

<!-- Load d3.js -->
<script src="https://d3js.org/d3.v6.js"></script>

<!-- Load Leaflet -->
<link rel="stylesheet" href="https://unpkg.com/leaflet@1.3.4/dist/leaflet.css" integrity="sha512-puBpdR0798OZvTTbP4A8Ix/l+A4dHDD0DGqYW6RQ+9jxkRFclaxxQb/SJAWZfWAkuyeQUytO7+7N4QKrDh+drA==" crossorigin=""/>
<script src="https://unpkg.com/leaflet@1.3.4/dist/leaflet.js" integrity="sha512-nMMmRyTVoLYqjP9hrbed9S+FzjZHW5gY1TWCHA5ckwXZBadntCNs8kEqAWdrb9O7rxbCaA4lKTIWjDXZxflOcA==" crossorigin=""></script>

<!-- Create an element where the map will take place -->
<div id="mapid"></div>

<style>
#mapid { height: 400px; }
</style>

<script>
// mapid is the id of the div where the map will appear
var map = L
  .map('mapid')
  .setView([47, 2], 5);   // center position + zoom

// Add a tile to the map = a background. Comes from OpenStreetmap
L.tileLayer(
    'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
    attribution: 'Map data &copy; <a href="https://www.openstreetmap.org/">OpenStreetMap</a>',
    maxZoom: 6,
    }).addTo(map);

// Add a svg layer to the map
L.svg().addTo(map);

// Create data for circles:
var markers = [
  {long: 9.083, lat: 42.149}, // corsica
  {long: 7.26, lat: 43.71}, // nice
  {long: 2.349, lat: 48.864}, // Paris
  {long: -1.397, lat: 43.664}, // Hossegor
  {long: 3.075, lat: 50.640}, // Lille
  {long: -3.83, lat: 48}, // Morlaix
];

// Select the svg area and add circles:
d3.select("#mapid")
  .select("svg")
  .selectAll("myCircles")
  .data(markers)
  .enter()
  .append("circle")
    .attr("cx", function(d){ return map.latLngToLayerPoint([d.lat, d.long]).x })
    .attr("cy", function(d){ return map.latLngToLayerPoint([d.lat, d.long]).y })
    .attr("r", 14)
    .style("fill", "red")
    .attr("stroke", "red")
    .attr("stroke-width", 3)
    .attr("fill-opacity", .4)

// Function that update circle position if something change
function update() {
  d3.selectAll("circle")
    .attr("cx", function(d){ return map.latLngToLayerPoint([d.lat, d.long]).x })
    .attr("cy", function(d){ return map.latLngToLayerPoint([d.lat, d.long]).y })
}

// If the user change the map (zoom or drag), I update circle position:
map.on("moveend", update)

</script>

<script>

// mapid is the id of the div where the map will appear
const map = L
  .map('mapid')
  .setView([47, 2], 5);   // center position + zoom

// Add a tile to the map = a background. Comes from OpenStreetmap
L.tileLayer(
    'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
    attribution: 'Map data &copy; <a href="https://www.openstreetmap.org/">OpenStreetMap</a>',
    maxZoom: 6,
    }).addTo(map);

// Add a svg layer to the map
L.svg().addTo(map);

// Create data for circles:
const markers = [
  {long: 9.083, lat: 42.149}, // corsica
  {long: 7.26, lat: 43.71}, // nice
  {long: 2.349, lat: 48.864}, // Paris
  {long: -1.397, lat: 43.664}, // Hossegor
  {long: 3.075, lat: 50.640}, // Lille
  {long: -3.83, lat: 48}, // Morlaix
];

// Select the svg area and add circles:
d3.select("#mapid")
  .select("svg")
  .selectAll("myCircles")
  .data(markers)
  .join("circle")
    .attr("cx", d => map.latLngToLayerPoint([d.lat, d.long]).x)
    .attr("cy", d => map.latLngToLayerPoint([d.lat, d.long]).y)
    .attr("r", 14)
    .style("fill", "red")
    .attr("stroke", "red")
    .attr("stroke-width", 3)
    .attr("fill-opacity", .4)

// Function that update circle position if something change
function update() {
  d3.selectAll("circle")
    .attr("cx", d => map.latLngToLayerPoint([d.lat, d.long]).x)
    .attr("cy", d => map.latLngToLayerPoint([d.lat, d.long]).y)
}

// If the user change the map (zoom or drag), I update circle position:
map.on("moveend", update)

</script>

Steps:

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