On the map above there are two tile overlays visible. To make this possible it is important that the tile structure of both overlays are in a different folder. The advantage of this approach is that it makes it easy to choose (and implement) which map you want to see at a given zoom-level. You do this by just deleting the unwanted image files in tile structure.
The code below will show one of the maps.
<rd:tileOverlay images="img/overlays/411_1/" mapMinZoom="3" mapMaxZoom="9" opacity="0.75" leftUnderLat="15.9250093927" leftUnderLng="-98.6202653642" rightUpperLat="34.2288367998" rightUpperLng="-75.3072158051" />