title: How to add an overlay map to a base map in OSMdroid
body: <p>I'm writing an android map tile-based navigation app that uses OSM as map data source.</p>
  <p>As base map I use <code>MAPNIK</code>, so it looks like</p>
  <pre><code>private MapView myBaseMap;
  myBaseMap.setTileSource(TileSourceFactory.MAPNIK);
  </code></pre>
  <p>Now I want to overlay <code>myBaseMap</code> with the biking map for the larger Netherlands. The bike map on its own - so only the bike paths without a map background - would look like</p>
  <pre><code>private MapView myOverlayMap;
  myOverlayMap.setTileSource(TileSourceFactory.FIETS_OVERLAY_NL);
  </code></pre>
  <p>which is of course of little use.</p>
  <p>So I'm looking for a way to overlay <code>myOverlayMap</code> on <code>myBaseMap</code>. I tried using the same procedure as I used for adding objects of the <code>Marker</code> type to <code>myBaseMap</code>, which is</p>
  <pre><code>myBaseMap.getOverlays().add(myOverlayMap);
  </code></pre>
  <p>but that was rejected as the required reference type is <code>Overlay</code> (which <code>Marker</code> indeed extends), whereas <code>myOverlayMap</code> is of the <code>MapView</code> type.</p>
  <p>Thanks in advance for your advice.</p>
  <p><em>Follow-up questions</em>: the <code>Marker</code> objects in turn will of course need to appear &quot;overlayed&quot; on <code>myOverlayMap</code> and the opacity of <code>myOverlayMap</code> will probably need to be reduced. How can that be done?</p>
  <p>PS: &quot;fiets&quot; is Dutch for &quot;bicycle&quot;.</p>