geoVoronoi.hull()

Use geoVoronoi.hull to compute the convex hull of a set of points in spherical coordinates.

Countries are grouped by their (World Bank) subregion, and we extract the bounding box for each of them. Then we highlight the convex hull of the set of all corners of the bounding boxes.

(With a special treatment for Antarctica and French Guyane.)

Watch, drag, and zoom.

<!DOCTYPE html> 
<head>
  <meta charset="utf-8">
  <script src="https://unpkg.com/d3@7"></script>
  <script src="https://unpkg.com/d3-delaunay@6"></script>
  <script src="https://unpkg.com/d3-geo-voronoi@2"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    
    .countries path {
        stroke: white;
        stroke-width: 0.3;
        opacity: 0.95;
        fill: #dbdbdb;
    }
    
    .links {
        stroke: red;
        stroke-opacity: 0.8;
        stroke-width: 1px;
        /*stroke-dasharray: 1 4; */
        fill: none;
    }
    
    .polygons {
      stroke: #c7ff84;
      stroke-width: 4;
      fill: #c7ff84;
      fill-opacity: 0.3;
    }
    
    .links {
        stroke-linecap: round;
    }
    
    .site {
        fill: #ddd;
        stroke: #000;
        stroke-width: 0.5;
    }
</style>
<svg width="960" height="500"></svg>

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

svg = svg
    .append('g');

var projection = d3.geoOrthographic().scale(214),
    path = d3.geoPath().projection(projection).pointRadius(1);

var g = svg.append('g')
    .attr('class', 'world')
    .append('g')
    .attr("class", "s");

var defs = g.append("defs");

defs.append("path")
    .datum({
        type: "Sphere"
    })
    .attr("id", "sphere")
    .attr("d", path);

g.append("use")
    .attr("xlink:href", "#sphere")
    .attr("fill", "#fcfcff");

defs.append("clipPath")
    .attr("id", "clip")
    .append("use")
    .attr("xlink:href", "#sphere");

g.attr("clip-path", "url(#clip)")

g.append('g')
    .attr('class', 'countries');

g.append("g")
    .attr("class", "polygons")

var site = g.append("g")
    .attr("class", "site")
    .selectAll('path')
    .data([null]);
var enter = site
    .enter() 
    .append('path');
site = site.merge(enter);

var legend = svg
    .append('text')
    .attr('transform', 'translate(' + [width / 2, 30] + ')')
    .attr('class', 'legend')
    .attr('text-anchor', 'middle')
    .attr('font-size', '20px')
    .attr('font-family', 'Helvetica');

var drag = 0;

d3.json('countries.geojson').then(function (world) {
        var visit = 0;
        var countries = d3.select('.countries')
            .selectAll('path')
            .data(world.features)
        .join('path')
            .attr('d', path)

var subregions = [...new Set(world.features.map(d => d.properties.subregion))];

go(countries, subregions[visit]);

d3.interval(visitnext, 1200)

function visitnext() {
            if (drag) return;
            visit = (visit + 1) % subregions.length;
            go(countries, subregions[visit]);
        }
    });

function go(countries, subregion) {

legend.text('The convex hull of ' + (subregion == 'Caribbean' || subregion == 'Seven seas (open ocean)' ? 'the ' : '') + subregion)

var sites = [],
        centroids = [];

countries.data()
        .filter(function (d) {
            return d.properties.subregion == subregion;
        })
        .map(function (d) {
            // remove French Guyane for the computation of bounds
            var e = JSON.parse(JSON.stringify(d));
            if (e.properties.iso_a3 == 'FRA') {
                e.geometry.coordinates = d.geometry.coordinates.slice(2);
            }
            return e;
        })
        .map(function (d) {
            var convex = d3.geoBounds(d);
            sites.push(convex[0]);
            sites.push(convex[1]);
            sites.push([convex[0][0], convex[1][1]]);
            sites.push([convex[1][0], convex[0][1]]);
            centroids.push(d3.geoCentroid(d));
        });

var hull = d3.geoVoronoi().hull(sites);

// special case, sorry!
    if (subregion == "Antarctica") {
        hull = d3.geoCircle().center([0, -90]).radius(29)();
    }

var rotation = d3.geoCentroid({
            type: 'MultiPoint',
            coordinates: sites
        })
        .map(function (x) {
            return -x;
        });

projection.rotate(rotation);

countries.attr("d", path);

d3.select('.polygons path').remove();
    var poly = d3.select('.polygons')
        .append("path")
        .datum(hull)
        .attr('d', path);

site.datum({
            type: "MultiPoint",
            coordinates: sites
        });

function draw() {
        poly.attr('d', path);
        countries.attr("d", path);
        site.attr('d', path)
    }

draw();

// drag and zoom
    svg.select('.world')
        .call(d3.drag()
            .on("start", dragstarted)
            .on("drag", dragged)
            .on("end", dragended)
        )
        .call(d3.zoom()
            .scaleExtent([1, 8])
            .on("zoom", zoomed)
            .on("start", function () {
                drag++;
            })
            .on("end", function () {
                setTimeout(function () {
                    drag--;
                }, 1500);
            })
        );

function zoomed({transform}) {
        svg.select('.world').attr("transform", transform);
    }

function dragstarted(event) {
        drag++;
        q = projection.rotate();
        r = d3.pointer(event);
    }

function dragended() {
        setTimeout(function () {
            drag--;
        }, 2000);
    }

var lambda = d3.scaleLinear()
        .domain([0, width])
        .range([-180, 180]);

var phi = d3.scaleLinear()
        .domain([0, height])
        .range([90, -90]);

function dragged(event) {
        var p = d3.pointer(event);
        projection.rotate([lambda(p[0]) - lambda(r[0]) + q[0], phi(p[1]) - phi(r[1]) + q[1]]);
        draw();
    }

}
</script>

https://unpkg.com/d3@7

https://unpkg.com/d3-delaunay@6

https://unpkg.com/d3-geo-voronoi@2