title: Plot/scatter position and marker size in the same coordinates
body: <p>I am trying to programmatically display various types of diagrams in pylab. pylab's scatter function displays markers at different co-ordinates in temrs of its axis, but the marker sizes are in terms of pixels. This makes sense for everyday graph plots. However, I want to give the co-ordinates and marker sizes in the same co-ordinates! e.g., the following code displays two circles at (0.0,0.0) and (0.5,0.5) with sizes of 20 each. These should overlap almost completely as the radius is much bigger than the distance between the centers. However, they don't because the sizes are in pixels while the positions are in terms of the axis coordinates.</p>
  
  <pre><code>import pylab
  pylab.scatter([0,0.5], [0,0.5], s=20, c='b', marker='o')
  </code></pre>
  
  <p>Is there a way to make a scatter plot (or draw any shapes, lines etc.) with the sizes and positions given in the same co-ordinates? I am interested in a vector graphics output (pdf, svg etc.).</p>