code: function() {
      this.map.unbind('change:view_bounds_sw',  null, this);
      this.map.unbind('change:view_bounds_ne',  null, this);
      this.map.unbind('change:zoom',            null, this);
      this.map.unbind('change:scrollwheel',     null, this);
      this.map.unbind('change:keyboard',        null, this);
      this.map.unbind('change:center',          null, this);
      this.map.unbind('change:attribution',     null, this);
    }
docs: unbind model properties