title: pyplot scatter plot marker size
body: <p>In the pyplot document for scatter plot:</p>
  
  <pre><code>matplotlib.pyplot.scatter(x, y, s=20, c='b', marker='o', cmap=None, norm=None,
                            vmin=None, vmax=None, alpha=None, linewidths=None,
                            faceted=True, verts=None, hold=None, **kwargs)
  </code></pre>
  
  <p>The marker size</p>
  
  <blockquote>
    <p>s:
    size in points^2. It is a scalar or an array of the same length as x and y.</p>
  </blockquote>
  
  <p>What kind of unit is <code>points^2</code>? What does it mean? Does <code>s=100</code> mean <code>10 pixel x 10 pixel</code>?</p>
  
  <p>Basically I'm trying to make scatter plots with different marker sizes, and I want to figure out what does the <code>s</code> number mean.</p>