D3 Examples - Force-directed cartogram

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v5.min.js"></script>
  <script src="https://unpkg.com/topojson@3"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>
​
<body>
  <div id="mapa" style="position: relative;left: 0; top: 0;">
    <canvas id='mapa_base' 
   style="position: absolute; left: 0; top: 0; z-index: 0;border: 2px solid green"></canvas>
    <canvas id='mapa_bolhas' 
            style="position: absolute; left: 0; top: 0; z-index: 1;border: 1px solid red"></canvas>
  </div>
  
  <script>
    const width = 800;
    const height = 800;
    
    const canvas_bolhas = d3.select("#mapa_bolhas")
      .attr("width", width)
      .attr("height", height);
    const canvasBase = d3.select("#mapa_base")
      .attr("width", width)
      .attr("height", height);
​
    const baseMapa = canvasBase.node().getContext("2d")
    const context = canvas_bolhas.node().getContext("2d");
    
    
    
    
    
    /*var svg = d3.select("body").append("svg")
      .attr("width", width)
      .attr("height", height) */
    
    const promises =                             
       [d3.json('municipios.json'), 
        d3.json('estados.json')]; 
​
    Promise.all(promises).then((values) => {
      const municipios = values[0];
      const estados = values[1];
      
      
      //const rio = municipios.filter(d => d.uf === "RJ")
      const rio = municipios.filter(d => d)
      const rio_base = topojson.feature(estados, estados.objects.BRUFE250GC_SIR);
      const rio_filtro = rio_base.features.filter(d=> d.properties.CD_GEOCUF == 33)[0]
      
      const extent = d3.extent(municipios, d=> d.pop2017)
      const maximo = extent[1]
      const escalaCor = d3.scaleLinear()
      const projecao = d3.geoMercator().fitSize([width, height], rio_base)
      const path = d3.geoPath().projection(projecao).context(baseMapa) //IMPORTANTE
      const tamanho = d3.scaleSqrt().domain(extent).range([1,20])
      const cor = d3.scaleOrdinal().domain([1,2,3,4]).range(d3.schemeSet1)
      
      const simulacao = d3.forceSimulation()
            .force('center', d3.forceCenter(width / 2, height / 2))
            .force('collision', d3.forceCollide(d => tamanho(d.pop2017)).iterations(2))
            .force('x', d3.forceX(d => projecao([d.lon,d.lat])[0]).strength(0.3))
            .force('y', d3.forceY(d => projecao([d.lon,d.lat])[1]).strength(0.3))
        .nodes(rio)
      
      /*const base = canvas.selectAll('.base_UF')
      .data([null])
      .enter() 
      .append('path')
      .attr('class', 'base_UF')
      .attr('d', path(rio_base))
      .style('fill', '#f2f2f2')
      */
        
      function drawBase(ctx){
        ctx.clearRect(0, 0, width, height);
        ctx.beginPath();
        ctx.fillStyle = '#f2f2f2';
        path(rio_base);
        ctx.fill();
        ctx.closePath();
        }
      
      
      /*const circulos = canvas.selectAll("circle.node")
            .data(municipios)
            .enter()
            .append("circle")
            .attr("class", "node")
        .attr('r', d => tamanho(d.pop2017))
        .style('fill', d => cor(d.venc))
        .style('stroke', 'red')
            .style("stroke-width", 0)
      
      circulos.append('title')
      .text(d => d.municipio)
      */
      
      
      
      drawBase(baseMapa);
      simulacao.on("tick", ticked)
      
      
      function ticked(){
        context.clearRect(0, 0, width, height);
        
       // draw nodes
    context.strokeStyle = "#fff";
    context.lineWidth = 0.5;
    municipios.forEach(function(d, i) {
      context.beginPath();
      context.fillStyle = cor(d.venc);
      context.moveTo(d.x, d.y);
      context.arc(d.x, d.y, tamanho(d.pop2017), 0, 2 * Math.PI);
      context.stroke();
      context.fill();
      context.closePath();
      
    });
      
    
        
        /*d3.selectAll("circle.node")
            .attr("cx", d => d.x)
            .attr("cy", d => d.y)
          
          */
      }
      
​
    })
    
​
  </script>
</body>
​
    