code: public static List<String> getVisibleServerLayerIds(MapModel mapModel) {
  		List<String> layerIds = new ArrayList<String>();
  		for (VectorLayer layer : mapModel.getVectorLayers()) {
  			if (layer.isShowing()) {
  				layerIds.add(layer.getServerLayerId());
  			}
  		}
  		return layerIds;
  	}
docs: Get a list of all visible layers on the given {@link MapModel}.
  
  @param mapModel map model
  @return a list of all visible layers.