D3 Examples - svg circles drawn for points maintain scale on zoom

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
body {
  margin: 0;
}
​
#container {
  position: relative;
  overflow: hidden;
    background: #ddd;
}
​
#map{
    width:100%;
    height:100%;
}
​
#points{
    width:100%;
    height:100%;
    position:relative;
    z-index:100;
}
​
.layer {
  position: absolute;
}
​
.tile {
  pointer-events: none;
  position: absolute;
  width: 256px;
  height: 256px;
}
​
.coffee{
    opacity: 0.8;
    fill: #ff2200;
}
​
.coffee:hover{
    opacity: 1.0;
    fill: #ff8a00;
}
​
.d3-tip {
  line-height: 1.5;
  font-weight: normal;
    font-family: Helvetica, Arial, sans-serif;
    font-size:13px;
  padding: 10px;
  background: rgba(0, 0, 0, 0.8);
  color: #fff;
  border-radius: 3px;
    position:relative;
    z-index:101;
}
​
/* Creates a small triangle extender for the tooltip */
.d3-tip:after {
  box-sizing: border-box;
  display: inline;
  font-size: 20px;
  width: 100%;
  line-height: .5;
  color: rgba(0, 0, 0, 0.8);
  content: "\25BC";
  position: absolute;
  text-align: center;
}
​
/* Style northward tooltips differently */
.d3-tip.n:after {
  margin: -1px 0 0 0;
  top: 100%;
  left: 0;
}
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/d3.geo.tile.v0.min.js"></script>
<script src="d3.tip.js"></script>
​
<script>
​
var width = Math.max(960, window.innerWidth),
    height = Math.max(500, window.innerHeight),
    prefix = prefixMatch(["webkit", "ms", "Moz", "O"]);
​
      d3.csv("coffee.csv", function(error, dataset) { createMap(dataset) });
​
var tile = d3.geo.tile()
    .size([width, height]);
​
var projection = d3.geo.mercator()
.scale((1 << 23) / 2 / Math.PI)
.translate([-width / 2, -height / 2]); // just temporary
​
var tileProjection = d3.geo.mercator();
​
var tilePath = d3.geo.path()
    .projection(tileProjection);
​
var zoom = d3.behavior.zoom()
    .scale(projection.scale() * 2 * Math.PI)
    .scaleExtent([1 << 9, 1 << 25])
    .translate(projection([-73.978277, 40.6791989]).map(function(x) { return -x; }))
    .on("zoom", zoomed);
        
var container = d3.select("body").append("div")
    .attr("id", "container")
    .style("width", width + "px")
    .style("height", height + "px")
    .call(zoom);
​
var map = container.append("g")
        .attr("id", "map")
​
var points = container.append("svg")
        .attr("id", "points")
                
var layer = map.append("div")
    .attr("class", "layer");
​
var tip = d3.tip()
      .attr('class', 'd3-tip')
      .offset([-10, 0])
      .html(function(d) { return "<img src='img/" + d.img + "' class='treeimg'>" + d.num + ". " + d.name + "<br/>(" + d.genus + " " + d.species + ")"; })
​
var tip = d3.tip()
    .attr('class', 'd3-tip')
        .offset([-10, 0])
        .html(function(d) { return d.name; })
​
points.call(tip);
​
zoomed();
​
function createMap(dataset) {
    d3.select("#points").selectAll("circle").data(dataset) //plotted    locations on map
    .enter()
    .append("circle")
    .attr("cx", function(d) {return projection([d.y,d.x])[0]})
    .attr("cy", function(d) {return projection([d.y,d.x])[1]})
    .attr("class", "coffee")
    .on('mouseover', tip.show)
    .on('mouseout', tip.hide)   
    zoomed();
}
​
function zoomed() {
  var tiles = tile
      .scale(zoom.scale())
      .translate(zoom.translate())
      ();
​
  projection
      .scale(zoom.scale() / 2 / Math.PI)
      .translate(zoom.translate());
​
var circles = d3.selectAll("circle")
                            .attr("cx", function(d) {return projection([d.y,d.x])[0]})
                            .attr("cy", function(d) {return projection([d.y,d.x])[1]})
                        .attr("r", .0000012*zoom.scale());
            
  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.se/hydda/full/" + 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 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>
</body>
</html>
    