problem with setting global variable

<script>
 $(document).ready(function() {
    // var pic = 'http://muzeum.pyramidlab.pl/uploads/Maps/muzeum.jpg';
    var pic;
        $('#Exhibits_isVisible').change(function(){
        if($('#Exhibits_isVisible').is(':checked'))
            $(this).attr('value','1');
        else
           $(this).attr('value','0');
       });

        display = function(value) {
       // $('#test').html("Id wybranej mapy: " + value);
       /*$.getJSON( ", function( data ) {
        console.log(data);
        $('#test').html("URl wybranej mapy: " + data);
       });*/
        $.ajax({
            //dataType: "json",
            url: "<?php echo $this->createUrl('/map/getPictureMapById') ?>/id/" +  value,
            success: function(data){
               // console.log(data);
                //$('#test').html("URl wybranej mapy: " + data);
                pic = data;
                console.log(pic);
            }
        });
    };

       function invokeMap(){
        var floorOverlay;
        var centerOfTheMap = new google.maps.LatLng(51.246613, 22.567874);
        var swBound = new google.maps.LatLng(51.245522, 22.565557);
        var neBound = new google.maps.LatLng(51.247403, 22.569746);
        var imageBounds = new google.maps.LatLngBounds(swBound, neBound);

            var allowedBounds = new google.maps.LatLngBounds(
                      new google.maps.LatLng(51.246294, 22.567010),
                      new google.maps.LatLng(51.246926, 22.568571)
                    );
        var mapOptions = {
                zoom: 19,
                zoomControl: false,
                scrollwheel: false,
                disableDefaultUI: true,
                disableDoubleClickZoom: true,
                center: centerOfTheMap
              };
        var map = new google.maps.Map(document.getElementById('map'),
                  mapOptions);
        var boundLimits = {
                        maxLat : allowedBounds.getNorthEast().lat(),
                        maxLng : allowedBounds.getNorthEast().lng(),
                        minLat : allowedBounds.getSouthWest().lat(),
                        minLng : allowedBounds.getSouthWest().lng()
                    };

                    var lastValidCenter = map.getCenter();
                    var newLat, newLng;
                    google.maps.event.addListener(map, 'center_changed', function() {
                        center = map.getCenter();

                        if (allowedBounds.contains(center)) {
                            lastValidCenter = map.getCenter();
                            return;
                        }

                        newLat = lastValidCenter.lat();
                        newLng = lastValidCenter.lng();
                        if(center.lng() > boundLimits.minLng && center.lng() < boundLimits.maxLng){
                            newLng = center.lng();
                        }
                        if(center.lat() > boundLimits.minLat && center.lat() < boundLimits.maxLat){
                            newLat = center.lat();
                        }
                        map.panTo(new google.maps.LatLng(newLat, newLng));

                    });

                        var marker = new google.maps.Marker({
                        position: centerOfTheMap,
                        map: map,
                        draggable:true,
                        //title:""
                           });

                    function countBounds() {
                        var mapBounds = map.getBounds();
                        var lewyDolny = mapBounds.getSouthWest();
                        var prawyGorny = mapBounds.getNorthEast();
                        var lewo    = mapBounds.lng();
                        var prawo   = mapBounds.lng();
                        var gora    = mapBounds.lat();
                        var dol     = mapBounds.lat();
                        var prawyDolny  = new google.maps.LatLng(dol,prawo);
                        var lewyGorny   = new google.maps.LatLng(gora,lewo);
                    }
                        google.maps.event.addListener(marker, 'dragend', function (event) {
                       document.getElementById("Exhibits_mapPositionX").value = this.getPosition().lat();
                       document.getElementById("Exhibits_mapPositionY").value = this.getPosition().lng();
                       });
                          floorOverlay = new google.maps.GroundOverlay(
                     // 'http://muzeum.pyramidlab.pl/uploads/Maps/muzeum.jpg',
                    pic,
                                        imageBounds);
              floorOverlay.setMap(map);
                          console.log(pic);
                      };
                      invokeMap();
    });

</script>