D3 Examples - OK Choropleth

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
  .county-border {
        fill: none;
        stroke: white;
        pointer-events: none;
    }
    .axis text {
        font: 10px sans-serif;
    }
​
    .axis line, .axis path {
        fill: none;
        stroke: #000;
        shape-rendering: crispEdges;
    }
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<script>
    //choropleth
        var width = 800, height = 400;
​
        var color = d3.scale.linear().domain([1.9, 42]).range(["#FEE8C8", "#B30000"]);
​
        var projection = d3.geo.conicConformal().parallels([35 + 34 / 60, 90 + 46 / 60]).rotate([98 + 00 / 60, -35 + 00 / 60]).translate([width / 2, height / 2]);
​
        var path = d3.geo.path().projection(projection);
​
        var svg = d3.select("body").append("svg").attr("width", width).attr("height", height);
​
        d3.json("ok-countiesHispanic.json", function(error, ok) {
            var counties = topojson.feature(ok, ok.objects.counties);
​
            projection.scale(1).translate([0, 0]);
​
            var b = path.bounds(counties), s = .95 / Math.max((b[1][0] - b[0][0]) / width, (b[1][1] - b[0][1]) / height), t = [(width - s * (b[1][0] + b[0][0])) / 2, (height - s * (b[1][1] + b[0][1])) / 2];
​
            projection.scale(s).translate(t);
​
            svg.selectAll("path").data(counties.features.filter(function(d) {
                return d.id;
            })).enter().append("path").attr("class", "county").attr("d", path).style("fill", function(d) {
                return color(d.properties.percent);
            }).append("title").text(function(d) {
                return d.properties.percent + "% of the population is hispanic. Estimated number of hispanic: " + d.properties.number;
            });
​
            svg.append("path").datum(topojson.mesh(ok, ok.objects.counties, function(a, b) {
                return a !== b;
            })).attr("class", "county-border").attr("d", path);
        });
        //end choropleth
​
        //key
        var w = 140, h = 400;
​
        var key = d3.select("body").append("svg").attr("id", "key").attr("width", w).attr("height", h);
​
        var legend = key.append("defs").append("svg:linearGradient").attr("id", "gradient").attr("x1", "100%").attr("y1", "0%").attr("x2", "100%").attr("y2", "100%").attr("spreadMethod", "pad");
​
        legend.append("stop").attr("offset", "0%").attr("stop-color", "#B30000").attr("stop-opacity", 1);
​
        legend.append("stop").attr("offset", "100%").attr("stop-color", "#FEE8c8").attr("stop-opacity", 1);
​
        key.append("rect").attr("width", w - 100).attr("height", h - 100).style("fill", "url(#gradient)").attr("transform", "translate(0,10)");
​
        var y = d3.scale.linear().range([300, 0]).domain([1, 42]);
​
        var yAxis = d3.svg.axis().scale(y).orient("right");
​
        key.append("g").attr("class", "y axis").attr("transform", "translate(41,10)").call(yAxis).append("text").attr("transform", "rotate(-90)").attr("y", 30).attr("dy", ".71em").style("text-anchor", "end").text("% Hispanic");
        //end key
        
        d3.select(self.frameElement).style("height", height + "px");
​
    </script>
    