Automatic Label Placement

This example is an extension of Mike Bostock’s tutorial Lets Make a Map that implements automatic label placement using the force layout and multiple foci. The centroid of each feature will define a foci of the force. This foci will attract the label that correspond to that feature (and ignore the others). The labels will repel themselves to avoid overlapping.

References

forked from pnavarrc's block: Automatic Label Placement

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8"/>
    <title>Automatic Label Placement</title>
    <script src="https://d3js.org/d3.v3.min.js"></script>
    <script src="https://d3js.org/topojson.v1.min.js"></script>

.subunit.IRL,
        .subunit-label.IRL {
            display: none;
        }

.subunit-boundary {
            fill: none;
            stroke: #777;
            stroke-dasharray: 2,2;
            stroke-linejoin: round;
        }

.subunit-boundary.IRL {
            stroke: #aaa;
        }

.subunit-label {
            fill: #777;
            fill-opacity: .5;
            font-size: 20px;
            font-weight: 300;
            text-anchor: middle;
        }

.place,
        .place-label {
            fill: #444;
        }

text {
            font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
            font-size: 10px;
            pointer-events: none;
        }
    </style>
</head>

<body>
<script>
    var width = 960,
        height = 1160;

var projection = d3.geo.albers()
        .center([0, 55.4])
        .rotate([4.4, 0])
        .parallels([50, 60])
        .scale(1200 * 5)
        .translate([width / 2, height / 2]);

var path = d3.geo.path()
        .projection(projection)
        .pointRadius(2);

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

d3.json("uk.json", function(error, uk) {

var subunits = topojson.feature(uk, uk.objects.subunits),
        places = topojson.feature(uk, uk.objects.places);

svg.selectAll(".subunit")
            .data(subunits.features)
            .enter().append("path")
            .attr("class", function(d) { return "subunit " + d.id; })
            .attr("d", path);

svg.append("path")
            .datum(topojson.mesh(uk, uk.objects.subunits, function(a, b) { return a !== b && a.id !== "IRL"; }))
            .attr("d", path)
            .attr("class", "subunit-boundary");

svg.append("path")
            .datum(topojson.mesh(uk, uk.objects.subunits, function(a, b) { return a === b && a.id === "IRL"; }))
            .attr("d", path)
            .attr("class", "subunit-boundary IRL");

svg.selectAll(".subunit-label")
            .data(subunits.features)
            .enter().append("text")
            .attr("class", function(d) { return "subunit-label " + d.id; })
            .attr("transform", function(d) { return "translate(" + path.centroid(d) + ")"; })
            .attr("dy", ".35em")
            .text(function(d) { return d.properties.name; });

svg.append("path")
            .datum(places)
            .attr("d", path)
            .attr("class", "place");

// Place and label location
        var foci = [],
            labels = [];

// Store the projected coordinates of the places for the foci and the labels
        places.features.forEach(function(d, i) {
            var c = projection(d.geometry.coordinates)
            foci.push({x: c[0], y: c[1]});
            labels.push({x: c[0], y: c[1], label: d.properties.name})
        });

console.log("foci", foci);
      	console.log("labels", labels);
      
        // Create the force layout with a slightly weak charge
        var force = d3.layout.force()
            .nodes(labels)
            .charge(-20)
            .gravity(0)
            .chargeDistance(width / 8)
            .size([width, height]);

// Append the place labels, setting their initial positions to
        // the feature's centroid
        var placeLabels = svg.selectAll('.place-label')
            .data(labels)
            .enter()
            .append('text')
            .attr('class', 'place-label')
            .attr('x', function(d) { return d.x; })
            .attr('y', function(d) { return d.y; })
            .attr('text-anchor', 'middle')
            .text(function(d) { return d.label; });

force.on("tick", function(e) {
            var k = .1 * e.alpha;
            labels.forEach(function(o, j) {
                // The change in the position is proportional to the distance
                // between the label and the corresponding place (foci)
                o.y += (foci[j].y - o.y) * k;
                o.x += (foci[j].x - o.x) * k;
            });

// Update the position of the text element
            svg.selectAll("text.place-label")
                .attr("x", function(d) { return d.x; })
                .attr("y", function(d) { return d.y; });
        });

force.start();
    });

</script>

</body>
</html>

https://d3js.org/d3.v3.min.js

https://d3js.org/topojson.v1.min.js