code: def initialize_ocean_and_thresholds(world, ocean_level=1.0):
      
      e = world.layers['elevation'].data
      ocean = fill_ocean(e, ocean_level)
      hl = find_threshold_f(e, 0.10)  # the highest 10% of all (!) land are declared hills
      ml = find_threshold_f(e, 0.03)  # the highest 3% are declared mountains
      e_th = [('sea', ocean_level),
              ('plain', hl),
              ('hill', ml),
              ('mountain', None)]
      harmonize_ocean(ocean, e, ocean_level)
      world.ocean = ocean
      world.elevation = (e, e_th)
      world.sea_depth = sea_depth(world, ocean_level)
docs: Calculate the ocean, the sea depth and the elevation thresholds
      :param world: a world having elevation but not thresholds
      :param ocean_level: the elevation representing the ocean level
      :return: nothing, the world will be changed