code: public TileBasedLayer createLayer(String id, TileConfiguration conf, final List<String> urls) {
  		return new AbstractTileBasedLayer(id, conf) {
  			@Override
  			public TileRenderer getTileRenderer() {
  				return new DefaultTileRenderer(urls);
  			}
  		};
  	}
docs: Create a new tile based layer with URLs to tile services.
  <p/>
  The URLs should have placeholders for the x- and y-coordinate and tile level in the form of {x}, {y}, {z}.
  The Y-coordinate can be inverted by specifying {-y} instead of {y}.
  The file extension of the tiles should be part of the URL.
  
  @param id   The unique ID of the layer.
  @param conf The tile configuration.
  @param urls The URLs to the tile services.
  @return A new tile based layer.