title: Why do we need to use flatMap?
body: <p>I am starting to use RxJS and I don't understand why in this example we need to use a function like <code>flatMap</code> or <code>concatAll</code>; where is the array of arrays here?</p>
  
  <pre><code>var requestStream = Rx.Observable.just('https://api.github.com/users');
  
  var responseMetastream = requestStream
    .flatMap(function(requestUrl) {
      return Rx.Observable.fromPromise(jQuery.getJSON(requestUrl));
    });
  
  responseMetastream.subscribe(url =&gt; {console.log(url)})
  </code></pre>
  
  <p>If someone can visually explain what is happening, it will be very helpful. </p>