title: how to control size of bubble in circle packing layout in d3
body: <p>in an animated circle packing d3 chart like this <a href="https://bl.ocks.org/HarryStevens/54d01f118bc8d1f2c4ccd98235f33848" rel="nofollow noreferrer">https://bl.ocks.org/HarryStevens/54d01f118bc8d1f2c4ccd98235f33848</a></p>
  
  <p>The bubble will always size to fill the rectangle drawing canvas. Is there a way to fix the size to be consistent such that I can make the bubble growing smaller? 
  <a href="https://i.stack.imgur.com/jhWWO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jhWWO.png" alt="enter image description here"></a></p>
  
  <p>meanwhile because it'll scale up, even if passing in smaller value, the radius doesn't really get smaller. </p>
  
  <p>for example: if data switched from [{"a",40}, {"b",50},{"c",60}] to 
   [{"a",4}, {"b",8},{"c",10}], ideally the circle get proportionally smaller.</p>
  
  <p>how to control the scale? thanks.</p>