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.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8"/>
<title>Automatic Label Placement</title>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<style>
.subunit.SCT { fill: #ddc; }
.subunit.WLS { fill: #cdd; }
.subunit.NIR { fill: #cdc; }
.subunit.ENG { fill: #dcd; }
.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})
});
// 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>