docs: def extend_extents(extents, factor=1.1):
      """Extend a given bounding box
  
      The bounding box (x1, y1, x2, y2) is centrally stretched by the given factor.
  
      :param extents: The bound box extents
      :param factor: The factor for stretching
      :return: (x1, y1, x2, y2) of the extended bounding box
      """
      width = extents[2] - extents[0]
      height = extents[3] - extents[1]
      add_width = (factor - 1) * width
      add_height = (factor - 1) * height
      x1 = extents[0] - add_width / 2
      x2 = extents[2] + add_width / 2
      y1 = extents[1] - add_height / 2
      y2 = extents[3] + add_height / 2
      return x1, y1, x2, y2