var layerNumShowing=1;

    function showLayerNumber(number)
                {

        var layerNumToShow=number;
                                lashow="la"+number;
                                lahide = "la"+layerNumShowing;
        document.getElementById(lashow).style.visibility = "visible";
        document.getElementById(lahide).style.visibility = "hidden";
        layerNumShowing=layerNumToShow;
    }