docs: def import_lv_load_areas(self, session, mv_grid_district, lv_grid_districts,
                               lv_stations):
          """Imports load_areas (load areas) from database for a single MV grid_district
  
          Parameters
          ----------
          session : sqlalchemy.orm.session.Session
              Database session
          mv_grid_district : MV grid_district/station (instance of MVGridDistrictDing0 class) for
              which the import of load areas is performed
          lv_grid_districts: DataFrame
              LV grid districts within this mv_grid_district
          lv_stations: :pandas:`pandas.DataFrame<dataframe>`
              LV stations within this mv_grid_district
          """
  
          # get ding0s' standard CRS (SRID)
          srid = str(int(cfg_ding0.get('geo', 'srid')))
          # SET SRID 3035 to achieve correct area calculation of lv_grid_district
          #srid = '3035'
  
          # threshold: load area peak load, if peak load < threshold => disregard
          # load area
          lv_loads_threshold = cfg_ding0.get('mv_routing', 'load_area_threshold')
  
          gw2kw = 10 ** 6  # load in database is in GW -> scale to kW
  
          # build SQL query
          lv_load_areas_sqla = session.query(
              self.orm['orm_lv_load_areas'].id.label('id_db'),
              self.orm['orm_lv_load_areas'].zensus_sum,
              self.orm['orm_lv_load_areas'].zensus_count.label('zensus_cnt'),
              self.orm['orm_lv_load_areas'].ioer_sum,
              self.orm['orm_lv_load_areas'].ioer_count.label('ioer_cnt'),
              self.orm['orm_lv_load_areas'].area_ha.label('area'),
              self.orm['orm_lv_load_areas'].sector_area_residential,
              self.orm['orm_lv_load_areas'].sector_area_retail,
              self.orm['orm_lv_load_areas'].sector_area_industrial,
              self.orm['orm_lv_load_areas'].sector_area_agricultural,
              self.orm['orm_lv_load_areas'].sector_share_residential,
              self.orm['orm_lv_load_areas'].sector_share_retail,
              self.orm['orm_lv_load_areas'].sector_share_industrial,
              self.orm['orm_lv_load_areas'].sector_share_agricultural,
              self.orm['orm_lv_load_areas'].sector_count_residential,
              self.orm['orm_lv_load_areas'].sector_count_retail,
              self.orm['orm_lv_load_areas'].sector_count_industrial,
              self.orm['orm_lv_load_areas'].sector_count_agricultural,
              self.orm['orm_lv_load_areas'].nuts.label('nuts_code'),
              func.ST_AsText(func.ST_Transform(self.orm['orm_lv_load_areas'].geom, srid)).\
                  label('geo_area'),
              func.ST_AsText(func.ST_Transform(self.orm['orm_lv_load_areas'].geom_centre, srid)).\
                  label('geo_centre'),
              (self.orm['orm_lv_load_areas'].sector_peakload_residential * gw2kw).\
                  label('peak_load_residential'),
              (self.orm['orm_lv_load_areas'].sector_peakload_retail * gw2kw).\
                  label('peak_load_retail'),
              (self.orm['orm_lv_load_areas'].sector_peakload_industrial * gw2kw).\
                  label('peak_load_industrial'),
              (self.orm['orm_lv_load_areas'].sector_peakload_agricultural * gw2kw).\
                  label('peak_load_agricultural'),
              ((self.orm['orm_lv_load_areas'].sector_peakload_residential
                + self.orm['orm_lv_load_areas'].sector_peakload_retail
                + self.orm['orm_lv_load_areas'].sector_peakload_industrial
                + self.orm['orm_lv_load_areas'].sector_peakload_agricultural)
               * gw2kw).label('peak_load')). \
              filter(self.orm['orm_lv_load_areas'].subst_id == mv_grid_district. \
                     mv_grid._station.id_db).\
              filter(((self.orm['orm_lv_load_areas'].sector_peakload_residential  # only pick load areas with peak load > lv_loads_threshold
                       + self.orm['orm_lv_load_areas'].sector_peakload_retail
                       + self.orm['orm_lv_load_areas'].sector_peakload_industrial
                       + self.orm['orm_lv_load_areas'].sector_peakload_agricultural)
                         * gw2kw) > lv_loads_threshold). \
              filter(self.orm['version_condition_la'])
  
          # read data from db
          lv_load_areas = pd.read_sql_query(lv_load_areas_sqla.statement,
                                            session.bind,
                                            index_col='id_db')
  
          # create load_area objects from rows and add them to graph
          for id_db, row in lv_load_areas.iterrows():
  
              # create LV load_area object
              lv_load_area = LVLoadAreaDing0(id_db=id_db,
                                             db_data=row,
                                             mv_grid_district=mv_grid_district,
                                             peak_load=row['peak_load'])
  
              # sub-selection of lv_grid_districts/lv_stations within one
              # specific load area
              lv_grid_districts_per_load_area = lv_grid_districts.\
                  loc[lv_grid_districts['la_id'] == id_db]
              lv_stations_per_load_area = lv_stations.\
                  loc[lv_stations['la_id'] == id_db]
  
              self.build_lv_grid_district(lv_load_area,
                                          lv_grid_districts_per_load_area,
                                          lv_stations_per_load_area)
  
              # create new centre object for Load Area
              lv_load_area_centre = LVLoadAreaCentreDing0(id_db=id_db,
                                                          geo_data=wkt_loads(row['geo_centre']),
                                                          lv_load_area=lv_load_area,
                                                          grid=mv_grid_district.mv_grid)
              # links the centre object to Load Area
              lv_load_area.lv_load_area_centre = lv_load_area_centre
  
              # add Load Area to MV grid district (and add centre object to MV gris district's graph)
              mv_grid_district.add_lv_load_area(lv_load_area)