actionscript 3 - How do I limit the area a movieclip can be dragged? -

i making interactive map in as3/flash cs6. @ moment, i've got zoom in , out, , dragged around.

but question is, how limit area map can dragged, can't see white space outside of it?

here code:

    import flash.events.mouseevent;      function initdragger(mc:movieclip):void     {         mc.addeventlistener(mouseevent.mouse_down, mousedownhandler);         mc.addeventlistener(mouseevent.mouse_up, mouseuphandler);       }      function mousedownhandler(e:mouseevent):void     {         e.currenttarget.startdrag();      }     function mouseuphandler(e:mouseevent):void     {         e.currenttarget.stopdrag();      }      // set drag     initdragger(map);      zoomin.addeventlistener(mouseevent.click, mapzoomin);      function mapzoomin(event:mouseevent):void     {         if (map.scalex < 10)         {             map.scalex +=  1;             map.scaley +=  1;         }      }      zoomout.addeventlistener(mouseevent.click, mapzoomout);      function mapzoomout(event:mouseevent):void     {         if (map.scalex > 1)         {             map.scalex -=  1;             map.scaley -=  1;         }      } 

the rectangle dimensions should in relation upper left corner of draggable item. if had 100x100 map , 50x50 viewable area, rectangle {x:-50, y:-50, width: 50, height:50}