code: def get_centroid_of_stops(gtfs):
      
      stops = gtfs.get_table("stops")
      mean_lat = numpy.mean(stops['lat'].values)
      mean_lon = numpy.mean(stops['lon'].values)
      return mean_lat, mean_lon
docs: Get mean latitude AND longitude of stops
  
      Parameters
      ----------
      gtfs: GTFS
  
      Returns
      -------
      mean_lat : float
      mean_lon : float