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@mbostock
Last active July 18, 2016 19:32
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Pseudo-Demers Cartogram
license: gpl-3.0

This is not a true Demers cartogram; it lacks links between adjacent features. Instead of trying to preserve connectedness, this pseudo-cartogram tries to preserve locality, putting each square as close as possible to its origin without overlapping.

<!DOCTYPE html>
<meta charset="utf-8">
<title>Demers Cartogram</title>
<style>
rect {
fill: #eee;
stroke: #000;
stroke-width: 1.5px;
}
</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
// Ratio of Obese (BMI >= 30) in U.S. Adults, CDC 2008
var valueById = [
NaN, 0.187, 0.198, NaN, 0.133, 0.175, 0.151, NaN, 0.100, 0.125,
0.171, NaN, 0.172, 0.133, NaN, 0.108, 0.142, 0.167, 0.201, 0.175,
0.159, 0.169, 0.177, 0.141, 0.163, 0.117, 0.182, 0.153, 0.195, 0.189,
0.134, 0.163, 0.133, 0.151, 0.145, 0.130, 0.139, 0.169, 0.164, 0.175,
0.135, 0.152, 0.169, NaN, 0.132, 0.167, 0.139, 0.184, 0.159, 0.140,
0.146, 0.157, NaN, 0.139, 0.183, 0.160, 0.143
];
var svg = d3.select("svg"),
margin = {top: 0, right: 0, bottom: 0, left: 0},
width = svg.attr("width") - margin.left - margin.right,
height = svg.attr("height") - margin.top - margin.bottom,
padding = 3;
var projection = d3.geoAlbersUsa();
var radius = d3.scaleSqrt()
.domain([0, d3.max(valueById)])
.range([0, 30]);
d3.json("us-state-centroids.json", function(error, states) {
if (error) throw error;
var nodes = states.features
.filter(function(d) { return !isNaN(valueById[+d.id]); })
.map(function(d) {
var point = projection(d.geometry.coordinates),
value = valueById[+d.id];
if (isNaN(value)) fail();
return {
x: point[0], y: point[1],
x0: point[0], y0: point[1],
r: radius(value),
value: value
};
});
var simulation = d3.forceSimulation()
.force("x", d3.forceX(function(d) { return d.x0; }))
.force("y", d3.forceY(function(d) { return d.y0; }))
.force("collide", collide)
.nodes(nodes)
.on("tick", tick);
var node = svg.selectAll("rect")
.data(nodes)
.enter().append("rect")
.attr("width", function(d) { return d.r * 2; })
.attr("height", function(d) { return d.r * 2; });
function tick(e) {
node.attr("x", function(d) { return d.x - d.r; })
.attr("y", function(d) { return d.y - d.r; });
}
function collide() {
for (var k = 0, iterations = 4, strength = 0.5; k < iterations; ++k) {
for (var i = 0, n = nodes.length; i < n; ++i) {
for (var a = nodes[i], j = i + 1; j < n; ++j) {
var b = nodes[j],
x = a.x + a.vx - b.x - b.vx,
y = a.y + a.vy - b.y - b.vy,
lx = Math.abs(x),
ly = Math.abs(y),
r = a.r + b.r + padding;
if (lx < r && ly < r) {
if (lx > ly) {
lx = (lx - r) * (x < 0 ? -strength : strength);
a.vx -= lx, b.vx += lx;
} else {
ly = (ly - r) * (y < 0 ? -strength : strength);
a.vy -= ly, b.vy += ly;
}
}
}
}
}
}
});
</script>
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