Plot points on map in Openlayers with USGS and Google Maps Support

openMap.js

/*
* @var lat = latitude
* @var lng = Longitude
* @var id = plotting multiple maps on a map
* If you are just using one map, you can remove the ID from here
* Logical function to plot points on openlayers map with support of USGS and Google Maps
*/
function openMap(lat, lng, id) {

    var layer;
    
    //GPS boundaries for USGS map     
    var layerExtent = new OpenLayers.Bounds(-20037508.34,-20037508.34,20037508.34,20037508.34);

    var options = {
      projection: new OpenLayers.Projection("EPSG:900913"),
      displayProjection: new OpenLayers.Projection("EPSG:4326"),
      units: "m",
      restrictedExtent: layerExtent
    };
    
    //If you are just plotting one point, you can remove the ID from here
    map[id] = new OpenLayers.Map( 'map'+id, options );
    
    //Next five "lines" define each layer the map supports    
    gphy = new OpenLayers.Layer.Google(
        "Google Terrain",
        {type: google.maps.MapTypeId.TERRAIN}
    );
    gmap = new OpenLayers.Layer.Google(
        "Google Streets", 
        {numZoomLevels: 20}
    );
    ghyb = new OpenLayers.Layer.Google(
        "Google Hybrid",
        {type: google.maps.MapTypeId.HYBRID, numZoomLevels: 20}
    );
    gsat = new OpenLayers.Layer.Google(
        "Google Satellite",
        {type: google.maps.MapTypeId.SATELLITE, numZoomLevels: 22}
    );

    topo = new OpenLayers.Layer.XYZ( 
        "USA Topo Map",
        "http://services.arcgisonline.com/ArcGIS/rest/services/USA_Topo_Maps/MapServer/tile/${z}/${y}/${x}",
        {sphericalMercator: true, numZoomLevels: 16} 
    );
    
    //Add each of the mapping capabilities
    map[id].addLayers([topo, gphy, gmap, ghyb, gsat]);
    
    var lonlat = new OpenLayers.LonLat(lng, lat).transform(
          new OpenLayers.Projection("EPSG:4326"), // transform from WGS 1984
          map[id].getProjectionObject() // to Spherical Mercator
    );
    
    //Define the style of the point
    vectors = new OpenLayers.Layer.Vector("Vector Layer", {
        styleMap: new OpenLayers.StyleMap({
                fillColor : 'red',
                fillOpacity : 0.8,                    
                strokeColor : "#ee9900",
                strokeOpacity : 1,
                strokeWidth : 1,
                pointRadius : 8
        })
    });            

    //Create the new point
    point = new OpenLayers.Geometry.Point(lonlat.lon, lonlat.lat);

    vectors.addFeatures([new OpenLayers.Feature.Vector(point)]);
    
    //Add the point as a new layer on the map
    map[id].addLayer(vectors);
    
    //Add the control navigiation to switch between Google maps and USGS topo map
    map[id].addControl(new OpenLayers.Control.LayerSwitcher());

    //Center the map on the point and do a zoom of 15
    map[id].setCenter(lonlat, 15 );

}