For some work I’m about to do I need to do some more advanced visualizations over maps but don’t really want to lose some of the functionality provided by Google Maps (as opposed to doing a pure d3 visualization which can be a little close to the metal when dealing with zooming/projections, etc.).

While researching this I discovered Google Maps + D3. This is a good start but I would like to place SVG elements all within a single SVG document so I can do things like animate relationships between them, etc. and this example generates one SVG per marker. In addition I want to be able to interact with the SVG elements so I need to them to be able to receive mouse events.

I’m pretty sure I’ve figured out nice ways to do both of these things. I copied (not forked) the source of Google Maps + D3 and the results can be found here.

The trick to using a single SVG (at least an approach here) was to pre-process all the markers and create an instance of google.maps.LatLngBounds that can then be used to determine how to size and position the SVG.


// Load the station data. When the data comes back, create an overlay.
d3.json("stations.json", function(data) {
  // fit the map to the boundaries of all available data points and
  // ONCE generate google LatLng objects to be re-used repeatedly
  var bounds = new google.maps.LatLngBounds();
    bounds.extend(d.value.lat_lng = new google.maps.LatLng(d.value[1], d.value[0]));
  var overlay = new google.maps.OverlayView(),
      r = 4.5,
      padding = r*2;
  // Add the container when the overlay is added to the map.
  overlay.onAdd = function() {
    var layer =
    overlay.draw = function(){
      var projection = this.getProjection(),
          sw = projection.fromLatLngToDivPixel(bounds.getSouthWest()),
          ne = projection.fromLatLngToDivPixel(bounds.getNorthEast());
      // extend the boundaries so that markers on the edge aren't cut in half
      sw.x -= padding;
      sw.y += padding;
      ne.x += padding;
      ne.y -= padding;'.stations')
        .attr('width',(ne.x - sw.x) + 'px')
        .attr('height',(sw.y - ne.y) + 'px')

Then when placing markers their position needs to just be adjusted by the values of sw.x and ne.y.


.attr('cx',function(d) {
  d = projection.fromLatLngToDivPixel(d.value.lat_lng);
  return d.x-sw.x;
.attr('cy',function(d) {
  d = projection.fromLatLngToDivPixel(d.value.lat_lng);
  return d.y-ne.y;

As for dealing with mouse events it turns out it’s just a matter of using the overlayMouseTarget layer instead of the overlayLayer.


overlay.onAdd = function() {
    var layer =