According to the Pāli canonical texts, sagga is not ‘heaven’ in spatial terms, in keeping with the early Buddhist non-cosmographical conceptions. It is described as a condition or state of birth: the beings reborn into heavenly conditions are described as devas (gods) and they are in the same spatial dimension as are human beings. The names of the different heavens, given as fourteen (consisting of the six lower heavens and the eight higher heavens) do not describe separate mini-worlds or compartments in space, but only different conditions of spiritual attainments by which alone they come to be distinguished.
"Sagga." The Concise Oxford Dictionary of World Religions. . Encyclopedia.com. (August 15, 2018). http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/sagga
"Sagga." The Concise Oxford Dictionary of World Religions. . Retrieved August 15, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/sagga