title: Highmaps: what is the code for a county?
body: <p>I am new to Highmaps and am playing with it.</p>
  
  <p>I notice that it uses the following data for a county in Maryland, USA.</p>
  
  <pre><code>Object { key="us-md-025",  value=23}]
  </code></pre>
  
  <p>I am curious about "025". What is it called?</p>