d3.geo.tiler = function() {
  var tiler = {},
      points = [],
      projection = d3.geo.mercator().scale(1).translate([.5, .5]),
      location = Object, // identity function
      zoom = 8,
      root = null;

  function build(points, x, y, z) {
    if (z >= zoom) return points.map(d3_geo_tilerData);
    var i = -1,
        n = points.length,
        c = [[], [], [], []],
        k = 1 << z++,
        p;
    while (++i < n) {
      p = points[i];
      var x1 = (p[0] * k - x) >= .5,
          y1 = (p[1] * k - y) >= .5;
      c[x1 << 1 | y1].push(p);
    }
    x <<= 1;
    y <<= 1;
    return {
      "0": c[0].length && build(c[0], x    , y    , z),
      "1": c[1].length && build(c[1], x    , y + 1, z),
      "2": c[2].length && build(c[2], x + 1, y    , z),
      "3": c[3].length && build(c[3], x + 1, y + 1, z)
    };
  }

  tiler.location = function(x) {
    if (!arguments.length) return location;
    location = x;
    root = null; // reset
    return tiler;
  };

  tiler.projection = function(x) {
    if (!arguments.length) return projection;
    projection = x;
    root = null; // reset
    return tiler;
  };

  tiler.zoom = function(x) {
    if (!arguments.length) return zoom;
    zoom = x;
    root = null; // reset
    return tiler;
  };

  tiler.points = function(x) {
    if (!arguments.length) return points;
    points = x;
    root = null; // reset
    return tiler;
  };

  tiler.tile = function(x, y, z) {
    var results = [];

    // Lazy initialization…
    // Project the points to normalized coordinates in [0, 1].
    if (!root) {
      root = build(points.map(function(d, i) {
        var point = projection(location.call(tiler, d, i));
        point.data = d;
        return point;
      }), 0, 0, 0);
    }

    function search(node, x0, y0, z0) {
      if (!node) return;
      if (z0 < z) {
        var k = Math.pow(2, z0 - z),
            x1 = (x * k - x0) >= .5,
            y1 = (y * k - y0) >= .5;
        search(node[x1 << 1 | y1], x0 << 1 | x1, y0 << 1 | y1, z0 + 1);
      } else {
        accumulate(node);
      }
    }

    function accumulate(node) {
      if (node.length) {
        for (var i = -1, n = node.length; ++i < n;) {
          results.push(node[i]);
        }
      } else {
        for (var i = -1; ++i < 4;) {
          if (node[i]) accumulate(node[i]);
        }
      }
    }

    search(root, 0, 0, 0);
    return results;
  };

  return tiler;
};

function d3_geo_tilerData(d) {
  return d.data;
}