D3 Examples - visualizing cities

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <title>SVG intro</title>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
 
  <style>
    
    body {
      background: black;
    }
    
    circle {
      fill: rgba(255, 255, 255, .5);
      stroke-opacity:0.5;
    }
    
    
   
  </style>
    
</head>
​
<body>
  
  
  <script>
   
    var outerWidth = 800;
    var outerHeight = 400;
    var margin = { left: -50, right:-50, top:0, bottom: 0};
    
    var innerWidth = outerWidth - margin.left - margin.right;
    var innerHeight = outerHeight - margin.top - margin.bottom;
    var circleRadius = 5;
    var xColumn = "longitude";
    var yColumn = "latitude";
    var rColumn = "population";
    var rMin = 0; rMax = 10;
    var r = 2;
    
    var svg = d3. select("body").append("svg")
        .attr("width", outerWidth)
        .attr("height", outerHeight);
    
    var g = svg.append('g')
        .attr('transform',"translate(" + margin.left + ", " + margin.top + ")");
    
    var xScale = d3.scale.linear().range([0,innerWidth]);
    var yScale = d3.scale.linear().range([innerHeight,0]);
    var rScale = d3.scale.sqrt().range([rMin,rMax]);  // make the area of the circle proportional to the size of the circle.
​
    
    function render(data) {
      xScale.domain(d3.extent(data, function(d) { return d[xColumn]; }));
      yScale.domain(d3.extent(data, function(d) { return d[yColumn]; }));
      rScale.domain([0, d3.max(data, function(d) { return d[rColumn]; })]);  // go from 0 to the max value
      
      var circles = g.selectAll("circle").data(data);
      circles.enter().append("circle").attr("r", circleRadius);
      
      circles
        .attr("cx",         function (d) { return     xScale(d[xColumn]); })
        .attr("cy",         function (d) { return     yScale(d[yColumn]); })
        .attr("r",          function (d) { return     rScale(d[rColumn]); })
      
      circles.exit().remove();
    }
    
    
    function type(d) {
            // name,latitude,longitude,population
​
      d.latitude = +d.latitude;
      d.longitude = +d.longitude;
      d.population = +d.population;
      return d;
    }
  
    d3.csv("cities.csv", type, render);
    
    
  </script>
</body>
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