Changing background map projection with d3.js





This post describes how to change the projection of your background map. (See here for explanations on basic map). Picking the right projection is a crucial step in your project, since shapes can be really different from one to the other and thus convey a different message. See this blog post to read more about it. This example works with d3.js v4 and v6


Background map section

Notes:

  • This code is very similar to the previous step: basic background map in d3

  • It just illustrate the possibilities of the geo-projection plugin.

  • Just pick the most appropriate one for your project: d3.geoAiry(), d3.geoAitoff(), d3.geoArmadillo(), d3.geoAzimuthalEqualArea(), d3.geoBaker(), d3.geoBoggs(), and many many more on the reference page.

  • Heavy data? It is a good practice to apply this transformation on the geoJson file directly -> avoid loading time in the browser.
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<!DOCTYPE html>
<meta charset="utf-8">

<!-- Load d3.js -->
<script src="https://d3js.org/d3.v4.js"></script>
<script src="https://d3js.org/d3-scale-chromatic.v1.min.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="400" height="300"></svg>

<!DOCTYPE html>
<meta charset="utf-8">
          
<!-- Load d3.js -->
<script src="https://d3js.org/d3.v6.js"></script>
<script src="https://d3js.org/d3-geo-projection.v3.min.js"></script>
          
<!-- Create an element where the map will take place -->
<svg id="my_dataviz" width="400" height="300"></svg>
      
<script>

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

// Map and projection. Try:  d3.geoAiry() / d3.geoAitoff() / d3.geoArmadillo() / d3.geoAugust() / d3.geoAzimuthalEqualArea() / d3.geoAzimuthalEquidistant() and more
var projection = d3.geoAitoff()
    .scale(width / 1.3 / Math.PI)
    .translate([width / 2, height / 2])

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

    // Draw the map
    svg.append("g")
        .selectAll("path")
        .data(data.features)
        .enter().append("path")
            .attr("fill", "#69b3a2")
            .attr("d", d3.geoPath()
                .projection(projection)
            )
            .style("stroke", "#fff")
})

</script>
<script>
// The svg
const svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height");

// Map and projection. Try:  d3.geoAiry() / d3.geoAitoff() / d3.geoArmadillo() / d3.geoAugust() / d3.geoAzimuthalEqualArea() / d3.geoAzimuthalEquidistant() and more
const projection = d3.geoAitoff()
    .scale(width / 1.3 / Math.PI)
    .translate([width / 2, height / 2])

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

    // Draw the map
    svg.append("g")
        .selectAll("path")
        .data(data.features)
        .join("path")
            .attr("fill", "#69b3a2")
            .attr("d", d3.geoPath()
                .projection(projection)
            )
            .style("stroke", "#fff")
})

</script>

Related blocks →

  • World Choropleth - link

  • Projection Transitions - link