Zoomable Map Tiles

A demo of the d3.geo.tile plugin, which determines which 256x256 tiles are visible in the viewport based on a scale and translate. This demo combines the tile plugin with d3.behavior.zoom for panning and zooming, resulting in a a simple slippy map. Based partly on an example by Tom MacWright.

Tiles copyright OpenStreetMap contributors.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  margin: 0;
}

.map {
  position: relative;
  overflow: hidden;
}

.layer {
  position: absolute;
}

.tile {
  pointer-events: none;
  position: absolute;
  width: 256px;
  height: 256px;
}

.info {
  position: absolute;
  bottom: 10px;
  left: 10px;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="d3.geo.tile.min.js"></script>
<script>

var width = Math.max(960, window.innerWidth),
    height = Math.max(500, window.innerHeight),
    prefix = prefixMatch(["webkit", "ms", "Moz", "O"]);

var tile = d3.geo.tile()
    .size([width, height]);

var projection = d3.geo.mercator();

var zoom = d3.behavior.zoom()
    .scale(1 << 12)
    .scaleExtent([1 << 9, 1 << 23])
    .translate([width / 2, height / 2])
    .on("zoom", zoomed);

var map = d3.select("body").append("div")
    .attr("class", "map")
    .style("width", width + "px")
    .style("height", height + "px")
    .call(zoom)
    .on("mousemove", mousemoved);

var layer = map.append("div")
    .attr("class", "layer");

var info = map.append("div")
    .attr("class", "info");

zoomed();

function zoomed() {
  var tiles = tile
      .scale(zoom.scale())
      .translate(zoom.translate())
      ();

projection
      .scale(zoom.scale() / 2 / Math.PI)
      .translate(zoom.translate());

var image = layer
      .style(prefix + "transform", matrix3d(tiles.scale, tiles.translate))
    .selectAll(".tile")
      .data(tiles, function(d) { return d; });

image.exit()
      .remove();

image.enter().append("img")
      .attr("class", "tile")
      .attr("src", function(d) { return "https://" + ["a", "b", "c"][Math.random() * 3 | 0] + ".tile.openstreetmap.org/" + d[2] + "/" + d[0] + "/" + d[1] + ".png"; })
      .style("left", function(d) { return (d[0] << 8) + "px"; })
      .style("top", function(d) { return (d[1] << 8) + "px"; });
}

function mousemoved() {
  info.text(formatLocation(projection.invert(d3.mouse(this)), zoom.scale()));
}

function matrix3d(scale, translate) {
  var k = scale / 256, r = scale % 1 ? Number : Math.round;
  return "matrix3d(" + [k, 0, 0, 0, 0, k, 0, 0, 0, 0, k, 0, r(translate[0] * scale), r(translate[1] * scale), 0, 1 ] + ")";
}

function prefixMatch(p) {
  var i = -1, n = p.length, s = document.body.style;
  while (++i < n) if (p[i] + "Transform" in s) return "-" + p[i].toLowerCase() + "-";
  return "";
}

function formatLocation(p, k) {
  var format = d3.format("." + Math.floor(Math.log(k) / 2 - 2) + "f");
  return (p[1] < 0 ? format(-p[1]) + "°S" : format(p[1]) + "°N") + " "
       + (p[0] < 0 ? format(-p[0]) + "°W" : format(p[0]) + "°E");
}

</script>

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