Chicago

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.zipcode {
  stroke: steelblue;
  fill: #FFF;
}
</style>

//Load in GeoJSON data
  d3.json("zipcodes.json", function(json) {

//Width and height
    var width = 900;
    var height = 450;

// create a first guess for the projection
    var center = d3.geo.centroid(json)
    var scale = 150;
    var projection = d3.geo.mercator().scale(scale).center(center);
    //Define path generator
    var path = d3.geo.path()
                    .projection(projection);

// using the path determine the bounds of the current map and use
    // these to determine better values for the scale and translation
    var bounds = path.bounds(json);
    var hscale = scale * width / (bounds[1][0] - bounds[0][0]);
    var vscale = scale * height / (bounds[1][1] - bounds[0][1]);
    var scale = (hscale < vscale) ? hscale : vscale;
    var offset = [width - (bounds[0][0] + bounds[1][0]) / 2,
                     height - (bounds[0][1] + bounds[1][1]) / 2];

// new projection
    projection = d3.geo.mercator().center(center)
     .scale(scale * 0.9).translate(offset);
    path = path.projection(projection);

//Create SVG element
    var svg = d3.select(".chart")
               .attr("width", width)
               .attr("height", height)

//Bind data and create one path per GeoJSON feature
    svg.selectAll("path")
      .data(json.features)
      .enter()
      .append("path")
      .attr("d", path)
      .attr("class", "zipcode");

});
</script>

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