Area shaded line chart

The lake elevation of Thunderbird for the last two years. The Line chart is rendered with D3, and has a red area underneath the average elevation.

<!DOCTYPE html>
<html>
<head>
<style>

body {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.x.axis path {
  display: none;
}

.area.above {
  fill: #E89B9B;
}

.area.below {
  fill: blue;
}

.line {
  fill: none;
  stroke: #000;
  stroke-width: 1.5px;
}

</style>
</head>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
var margin = {top: 20, right: 20, bottom: 30, left: 50},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var parseDate = d3.time.format("%b-%y").parse;

var x = d3.time.scale()
    .range([0, width]);

var y = d3.scale.linear()
    .range([height, 0]);

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom");

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left");

var line = d3.svg.area()
    .interpolate("basis")
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d["Thunderbird"]); });

var area = d3.svg.area()
    .interpolate("basis")
    .x(function(d) { return x(d.date); })
    .y1(function(d) { return y(d["Thunderbird"]); });

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 + ")");

d3.tsv("thunderbird.tsv", function(error, data) {
  data.forEach(function(d) {
    d.date = parseDate(d.date);
    d["Thunderbird"]= +d["Thunderbird"];
    d["Normal"] = +d["Normal"];
  });

x.domain(d3.extent(data, function(d) { return d.date; }));

y.domain([
    d3.min(data, function(d) { return Math.min(d["Thunderbird"], d["Normal"]); }),
    d3.max(data, function(d) { return (Math.max(d["Thunderbird"], d["Normal"]+1)); })
  ]);

svg.datum(data);

svg.append("clipPath")
      .attr("id", "clip-below")
    .append("path")
      .attr("d", area.y0(height));

svg.append("clipPath")
      .attr("id", "clip-above")
    .append("path")
      .attr("d", area.y0(0));

svg.append("path")
      .attr("class", "area above")
      .attr("clip-path", "url(#clip-above)")
      .attr("d", area.y0(function(d) { return y(d["Normal"]); }));

svg.append("path")
      .attr("class", "area below")
      .attr("clip-path", "url(#clip-below)")
      .attr("d", area);

svg.append("path")
      .attr("class", "line")
      .attr("d", line);

svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(1," + height + ")")
      .call(xAxis);

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("transform", "rotate(-90)")
      .attr("transform", "translate(50, 0)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Elevation");
      
       var legend = svg.selectAll(".legend")
      //.data(ageNames.slice().reverse())
   // .enter().append("g")
      .attr("class", "legend")
      .attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });

legend.append("rect")
      .attr("x", width - 18)
      .attr("width", 18)
      .attr("height", 18)
      .style("fill", "#E89B9B");

legend.append("text")
      .attr("x", width - 24)
      .attr("y", 9)
      .attr("dy", ".35em")
      .style("text-anchor", "end")
      .text(function(d) { return d; });
});

</script>
</body>
</html>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js