code: def aggregate_tile(cells, ti, tj, aggregate, params, metadata, layout, summary):
    
    tile = []
    keys = cells.keys()
    for i,key in enumerate(keys):
      print("cell", i+1, "/", len(keys), end='\r')
      cell_json = aggregate(cells[key], params, metadata, layout, summary)
      tile.append({"aggregate":cell_json, "i":int(key[0]), "j":int(key[1])})
    return tile
docs: Call the user defined aggregation function on each cell and combine into a single json object