Google Map (Grey) + D3

<!DOCTYPE html>
<html>
  <head>
    <meta name="viewport" content="initial-scale=1.0, user-scalable=no"/>
    <script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=true&libraries=visualization"></script>
    <script src="https://d3js.org/d3.v3.min.js"></script>
    <link href="https://fonts.googleapis.com/css?family=Open+Sans:400,700,300" rel='stylesheet' type='text/css'>
    <style type="text/css">

html, body, #map {
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;
}

.stations, .stations svg {
  position: absolute;
}

.stations svg {
  width: 60px;
  height: 20px;
  padding-right: 100px;
  font: 10px sans-serif;
}

.stations circle {
  fill: #00aeef;
  stroke: #00447c;
  stroke-width: 1px;
}

</style>
  </head>
  <body>
    <div id="map"></div>
    <script type="text/javascript">

// Create the Google Map…
var map = new google.maps.Map(d3.select("#map").node(), {
  zoom: 8,
  center: new google.maps.LatLng(37.76487, -122.41948),
  styles: [{stylers:[{saturation:-100},{gamma:1}]},{elementType:"labels.text.stroke",stylers:[{visibility:"off"}]},{featureType:"poi.business",elementType:"labels.text",stylers:[{visibility:"off"}]},{featureType:"poi.business",elementType:"labels.icon",stylers:[{visibility:"off"}]},{featureType:"poi.place_of_worship",elementType:"labels.text",stylers:[{visibility:"off"}]},{featureType:"poi.place_of_worship",elementType:"labels.icon",stylers:[{visibility:"off"}]},{featureType:"road",elementType:"geometry",stylers:[{visibility:"simplified"}]},{featureType:"water",stylers:[{visibility:"on"},{saturation:40},{gamma:0},{hue:"#00aeef"}]},{featureType:"administrative.neighborhood",elementType:"labels.text.fill",stylers:[{color:"#333333"}]},{featureType:"road.local",elementType:"labels.text",stylers:[{weight:0.5},{color:"#333333"}]},{featureType:"transit.station",elementType:"labels.icon",stylers:[{gamma:1},{saturation:50}]}],
  mapTypeId: google.maps.MapTypeId.ROADMAP //google.maps.MapTypeId.SATELLITE
});

// Load the station data. When the data comes back, create an overlay.
d3.json("stations.json", function(data) {
  var overlay = new google.maps.OverlayView();

// Add the container when the overlay is added to the map.
  overlay.onAdd = function() {
    var layer = d3.select(this.getPanes().overlayLayer).append("div")
        .attr("class", "stations");

// Draw each marker as a separate SVG element.
    // We could use a single SVG, but what size would it have?
    overlay.draw = function() {
      var projection = this.getProjection(),
          padding = 10;

var marker = layer.selectAll("svg")
          .data(d3.entries(data))
          .each(transform) // update existing markers
        .enter().append("svg:svg")
          .each(transform)
          .attr("class", "marker");

// Add a circle.
      marker.append("svg:circle")
          .attr("r", 4.5)
          .attr("cx", padding)
          .attr("cy", padding);

// Add a label.
      marker.append("svg:text")
          .attr("x", padding + 7)
          .attr("y", padding)
          .attr("dy", ".31em")
          .text(function(d) { return d.key; });

function transform(d) {
        d = new google.maps.LatLng(d.value[1], d.value[0]);
        d = projection.fromLatLngToDivPixel(d);
        return d3.select(this)
            .style("left", (d.x - padding) + "px")
            .style("top", (d.y - padding) + "px");
      }
    };
  };

// Bind our overlay to the map…
  overlay.setMap(map);
});

</script>
  </body>
</html>

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

https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=true&libraries=visualization

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