map.dataLayer = new OpenLayers.Layer("Data", { "visibility": false });
map.dataLayer.events.register("visibilitychanged", map.dataLayer, toggleData);
map.addLayer(map.dataLayer);
map.dataLayer = new OpenLayers.Layer("Data", { "visibility": false });
map.dataLayer.events.register("visibilitychanged", map.dataLayer, toggleData);
map.addLayer(map.dataLayer);