Hexbin Heightmap

Each cell takes the mean value as its color.

<!DOCTYPE html>
<meta charset="utf-8">
<style>
html, body {
  background: #000;
}
svg, canvas {
  position: absolute;
  top: 0;
  left: 0;
}
canvas {
  display: none;
}
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/d3.hexbin.v0.min.js"></script>
<script>

var width = 960,
    height = 500;

var hexbin = d3.hexbin()
    .size([width, height])
    .radius(5);

var color = d3.scale.linear()
   .domain([14, 15, 35, 132])
   .range(["#333", "#d7191c", "#ffffbf", "#2c7bb6"])
   .interpolate(d3.interpolateHcl);

var canvas = d3.select("body").append("canvas")
    .attr("width", width)
    .attr("height", height);

var context = canvas.node().getContext("2d");
var points = [];
var hexagons = [];

getImage("readme.png", function(image) {
  context.drawImage(image, 0, 0, width, height);
  image = context.getImageData(0, 0, width, height);

// Rescale the colors.
  for (var c, i = 0, n = width * height * 4, d = image.data; i < n; i += 4) {
    points.push([i/4%width, Math.floor(i/4/width), d[i]]);
  }

hexagons = hexbin(points);
  hexagons.forEach(function(d) {
    d.mean = d3.mean(d, function(p) { return p[2]; });
  });

var svg = d3.select("body").append("svg")
      .attr("width", width)
      .attr("height", height);

var hexagon = svg.append("g")
      .attr("class", "hexagons")
    .selectAll("path")
      .data(hexagons)
    .enter().append("path")
      .attr("d", hexbin.hexagon(4.5))
      .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; })
      .style("fill", function(d) { return color(d.mean); });
});

function getImage(path, callback) {
  var image = new Image;
  image.onload = function() { callback(image); };
  image.src = path;
}

</script>

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

Modified http://d3js.org/d3.hexbin.v0.min.js to a secure url

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

https://d3js.org/d3.hexbin.v0.min.js