code: def _overlay_union(df1, df2):
      """
      Overlay Union operation used in overlay function
      """
      dfinter = _overlay_intersection(df1, df2)
      dfsym = _overlay_symmetric_diff(df1, df2)
      dfunion = pd.concat(
          [dfinter, dfsym], ignore_index=True, sort=False
      )
      # keep geometry column last
      columns = list(dfunion.columns)
      columns.remove("geometry")
      columns.append("geometry")
      return dfunion.reindex(columns=columns)
  
file_path: geopandas/geopandas/tools/overlay.py
imports: import warnings
  from functools import reduce
  import numpy
  import pandas
  from geopandas import GeoDataFrame, GeoSeries
  from geopandas.array import _check_crs, _crs_mismatch_warn
label_desc: Use image node_id 5 for calling a global function with example usage: _overlay_union(df1, df2) and returns: dfunion