Gmaps with circles denoting quantities

I'd like to modify the default User Locations so as to avoid any user addresses being given away. I realise I can prevent zooming, but still results in too much information being given out.

One thing I saw years ago was using maps with quantities centred on UK postcodes (although could be cities, countries, etc.) with a bigger diameter circle meaning more people were based there. You had to draw the biggest circles first, but it looked really good and gives a great view of where your members are based without given much away about their actual location.

I found the page discussing the technique, but unfortunately the link is dead, so see attached example I've knocked up.

Anybody have any idea whether this is possible in Drupal and where you might start?