Japan Prefecture Population Change Since WW2

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    <meta charset="UTF-8">
    <script src="d3.min.js"></script>
    <script src="topojson.js"></script>
    <script src="d3.slider.js"></script>
    <link rel="stylesheet" type="text/css" href="d3.slider.css">
    <title>Japanese Regional Population Change After WW2 (5 Years Interval)</title>
    <style>
      
      #tooltip {
        position: absolute;
        top: 0;
        left: 0;
        background-color: lightsteelblue;
        text-align: center;
        padding: 5px;
      }

.wrapper{
        max-width: 90%;
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body {
        font-family: Helvetica, Arial, sans-serif;
        background-color: #eee;
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#maintext {
        width: 1000px;
        margin: 25px auto 25px auto;
        padding: 50px 50px 50px 50px;
        background-color: white;
        box-shadow: 0 0 20px #ccc;
      }

h1 {
        margin-bottom: 25px;
        font-size: 24px;
        font-weight: bold;
      }

h4 {
        margin-top: 30px;
        margin-left: 20px;
        font-size: 14px;
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p {
        margin-bottom: 25px;
        font-size: 13px;
        line-height: 18px;
      }

</style>
  </head>
  <body>

<h1>Japanese Regional Population Change After WW2 (5 Years Interval)</h1>
      <h4>Unit: Thousands people</h4>
      
      <p>The graph shows the trend of Japanese population growth since WW2. As the reader moves the slider towards present days. It shows the population growth is moving into negative territory in most areas, except Tokyo and Osaka region. Also it shows a huge growth in some regions right after the war, and the urbanization of Tokyo since the end of war. For more information, please refer to README.md file.<p>

var japan;
    var keys; // variable for different key(prefecture)
    var currentKey; // variable for current selection key (year)
    var sliderKeys = []; // year variable for sliders 
    var w = 960;
    var h = 760;
    
    // Setup canvas/container
    var container = d3.select('.container');
    var svg = container.append('svg')
        .attr('width', w)
        .attr('height', h)
        .append("g");

var g = svg.append("g");

// Assign color to domain range
    var color = d3.scale.linear()
        .domain([-150, 0, 500, 1000, 1800])
        .range(['#feebe2', '#fbb4b9', '#f768a1', '#c51b8a', '#7a0177']);

// Tooltip style
    var tooltip = d3.select("body")
                    .append("div")
                    .attr("id", "tooltip")
                    .style("opacity", 0);

// Update map color function
    var updateMap = function() {
      g.selectAll('path')
        .transition()
        .duration(1000)
        .style('fill', function(d) {
          return color(d.properties[currentKey]);
        });
    }

// Legend color
    svg.selectAll('rect.legend')
      .data(color.domain())
      .enter()
      .append('rect')
      .attr('class', 'legend')
      .attr('x', 65)
      .attr('y', function(d, i) { return 100 + 20 * i; })
      .attr('width', 20)
      .attr('height', 20)
      .attr('fill', function(d) { return color(d); });
    
    // Legend text
    svg.selectAll('text.legend')
      .data(color.domain())
      .enter()
      .append('text')
      .attr('x', 60)
      .attr('y', function(d, i) { return 100 + 20 * i + 12; })
      .attr('font-size', 9)
      .attr('text-anchor', 'end')
      .text(function(d) { return d; });

// Read map file
    d3.json('japan.topojson', function(error, collection) {
      var japan = topojson.feature(collection, collection.objects.japan).features;

// Setup map
      var projection = d3.geo.mercator()
                         .scale(1500)
                         .center([137, 35])
                         .translate([w / 2, h / 2]);
      var path = d3.geo.path().projection(projection);

g.selectAll('path')
        .data(japan)
        .enter()
        .append('path')
        .attr('d', path)
        .attr('prefecture', function(d) {
          return d.properties.name;
        })
        .style('fill', function(d, i) {
          return 'white';
        })
        .attr("stroke", "#404040")
        .attr("stroke-width", 0.5)
        .style('cursor', 'pointer')
        .on('mouseover', function(d){ // Mouse over action
          tooltip.style("opacity", 1)
            .html(d.properties['name']+'<br/>'+d.properties[currentKey])
            .style("left", (d3.event.pageX + 10) + "px")
            .style("top", (d3.event.pageY - 40) + "px");

// Read csv data 
        d3.csv('jp_pop.csv', function(error, rows) {

// Gather data from csv
          keys = Object.keys(rows[0]).filter(function(key){ return key !== 'prefecture'; });
          
          // Prepare sliderKeys for slider
          sliderKeys = svg.selectAll('.keys')
                          .data(keys)
                          .enter()[0]
                          .map(function(x) 
                          {
                            return x['__data__'] ;
                          });
   
          var total = sliderKeys.length,
              min = sliderKeys[0],
              difference = sliderKeys[1] - sliderKeys[0],
              max = sliderKeys[total-1];
          
          // Add a slider
          d3.select('.slider').call(
            d3.slider()
              .axis(true)
              .min(min)
              .max(max)
              .step(difference)
              .on("slide", function(evt, value) {
              currentKey = value;

d3.selectAll('.keys')
                .classed("selected", function(){return (d3.select(this).attr('value') === currentKey)});
              updateMap();
            })
          );

// Read population data for that year
          for (var i = 0; i < rows.length; i++) {
            var municipality = japan.filter(function(obj) {
              return (obj.properties['name'] === rows[i]['prefecture']);
            })[0];

if (municipality) {
              keys.forEach(function(key){
                municipality.properties[key] = rows[i][key];
              });
        		}
          }

// Set data to the first year when first load map
          currentKey = keys[0];
          updateMap();
        });
    });

</script>

</body>
</html>