title: County boarders in Cartopy
body: <p>How do you plot US county borders in Cartopy?</p>
  
  <p>It's very straight forward to plot state and country boundaries</p>
  
  <pre><code>ax.add_feature(cfeature.BORDERS.with_scale('50m'))
  ax.add_feature(cfeature.STATES.with_scale('50m'))
  </code></pre>
  
  <p>But I can't seem to find a similar method to add county boundaries. This was one of the nice things about Basemap.</p>