title: What is the necessity of plt.figure() in matplotlib?
body: <pre><code>plt.figure(figsize=(10,8))
  
  plt.scatter(df['attacker_size'][df['year'] == 298],
          # attacker size in year 298 as the y axis
          df['defender_size'][df['year'] == 298],
          # the marker as
          marker='x',
          # the color
          color='b',
          # the alpha
          alpha=0.7,
          # with size
          s = 124,
          # labelled this
          label='Year 298')
  </code></pre>
  
  <p>In the above snippet of code collected from <a href="http://chrisalbon.com/python/matplotlib_simple_scatterplot.html" rel="noreferrer">Scatterplot in Matplotlib</a>, what is the necessity of <code>plt.figure()</code>? </p>