code: function changedActiveItems(dataSource) {
    reviseLegendHelper(dataSource);
    updateEntitiesAndExtent(dataSource); // Only does anything if there are lat & lon columns.
    dataSource._changed.raiseEvent(dataSource);
  }
docs: Call when the active column changes, or when the table data source is first shown.
  Generates a LegendHelper.
  For lat/lon files, updates entities and extent.
  For region files, rebuilds and redisplays the regionImageryLayer.
  @private