Basic bubble map in d3.js




This post describes how to build a very basic bubble map with d3.js. It uses the previous background map of France, and add a few circles at specific coordinates on top of it. See more bubblemap examples here.


Bubble map section

Steps:

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

  • 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 the projection function needs to be applied to the circle X and Y coordinates
<!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>

<!-- Create an element where the map will take place -->
<svg id="my_dataviz" width="440" height="300"></svg>


<script>

// The svg
var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height");

// Map and projection
var projection = d3.geoMercator()
    .center([2, 47])                // GPS of location to zoom on
    .scale(1020)                       // This is like the zoom
    .translate([ width/2, height/2 ])


// 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: 58}, // Morlaix
];

// Load external data and boot
d3.json("https://raw.githubusercontent.com/holtzy/D3-graph-gallery/master/DATA/world.geojson", function(data){

    // Filter data
    data.features = data.features.filter( function(d){return d.properties.name=="France"} )

    // Draw the map
    svg.append("g")
        .selectAll("path")
        .data(data.features)
        .enter()
        .append("path")
          .attr("fill", "#b8b8b8")
          .attr("d", d3.geoPath()
              .projection(projection)
          )
        .style("stroke", "black")
        .style("opacity", .3)

    // Add circles:
    svg
      .selectAll("myCircles")
      .data(markers)
      .enter()
      .append("circle")
        .attr("cx", function(d){ return projection([d.long, d.lat])[0] })
        .attr("cy", function(d){ return projection([d.long, d.lat])[1] })
        .attr("r", 14)
        .style("fill", "69b3a2")
        .attr("stroke", "#69b3a2")
        .attr("stroke-width", 3)
        .attr("fill-opacity", .4)
})

</script>

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