title: React native MapView: what is latitudeDelta longitudeDelta
body: <p>In the example from <a href="https://github.com/react-community/react-native-maps/blob/master/README.md#mapview" rel="noreferrer">react native mapview</a> they have latitudeDelta and longitudeDelta. Is it equal to the height and width? And in what unit? Accoring to their <a href="https://github.com/facebook/react-native/blob/0.28-stable/Libraries/Components/MapView/MapView.js#L140" rel="noreferrer">github comment </a>, it says </p>
  
  <blockquote>
    <p>Distance between the minimum and the maximum latitude/longitude to be displayed.</p>
  </blockquote>
  
  <p>But that doesn't help me out. I want to know what the user see on the map.</p>