D3 Examples - Enclosing Force Circles

Enclosing Force Circles

Using d3.packEnclose to draw larger circles around circles forced towards a single point.

Visualising London university pay ratios. The number of dots in each enclosed circle indicates the ratio between the lowest and highest paid at each university. Hovering over each circle reveals the ratio.

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <script src="paygaps.js"></script>
  <style>
    body { margin: 0; position: fixed; top: 0; right: 0; bottom: 0; left: 0; }
    
    .enclosing-circle {
      fill-opacity: 0.05;
    }
    
  </style>
</head>
​
<body>
  <script>
    var margin = { top: 50, right: 50, bottom: 50, left: 50 };
    
    var width = 960 - margin.left - margin.right,
        height = 500 - margin.top - margin.bottom;
    
    var svg = d3.select("body").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    .append("g")
        .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
    var radius = 5;   
    
    var initPos = { x: 120, y: 100 },
        paddingX = 250,
        paddingY = 150;
    
    var rowLength = 8;
   
    function sortBy(attribute, order) {
        councils.sort(function(a, b) {
        if(a[attribute] < b[attribute]) return -1 * order;
        if(a[attribute] > b[attribute]) return 1 * order;
        return 0;
        });
    }
    
    councils.forEach(function(p, i) {
      var dots = d3.range(p.max).map(function(d) {
        return {
          circleId: i,
          id: d
        }
      });  
      
      var simulation = d3.forceSimulation(dots)
        .force("x", d3.forceX(initPos.x + paddingX * (i % rowLength)).strength(2))
        .force("y", d3.forceY(initPos.y + paddingY * (Math.floor(i / rowLength))).strength(1))
        .force("collide", d3.forceCollide(radius + 1).iterations(10))
        .stop(); 
      
        for (var x = 0; x < 120; ++x) simulation.tick();
      
        addCircles(dots, i);     
    })
​
    function addCircles(data, i) {
      
      var circles = svg.append("g")
        .attr("class", "circles")
        .selectAll("g").data(data)
      .enter().append("g")
        .each(function(d) {
            d.r = radius;
        })
        .style("fill", 'steelblue')
        .style('opacity', .8);
    
      circles.append("circle")
        .attr("r", radius)
        .attr("cx", function(d) {
          return d.x;
        })
        .attr("cy", function(d) {
          return d.y;
        });
      
      var enclosingCircleAttr = d3.packEnclose(circles.data());
      
      var enclosingCircle = svg.append("g")
        .append("circle")
        .datum(enclosingCircleAttr)
        .attr("class", "enclosing-circle")
        .attr("r", function(d) {
          return d.r + radius;
        })
        .attr("cx", function(d) {
          return d.x;
        })
        .attr("cy", function(d) {
          return d.y;
        })
​
​
    }
​
  </script>
</body>
​
    