user2225: And How the buddha know all of these things. I suppose he knew from meditation until enlighten? So it is possible that just by mediation alone one can know about other realm of existence.
http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html

user8157: There is a major principle in original Buddhism that the Dhamma (true reality) is experienced in the here-&-now (sanditthiko); has immediate results (akaliko); invites inspection (ehipassiko); leads to peace (opanayiko); & verified by the observant for themselves (paccattam veditabbo vinnuhi).  
MN 38 states disciples of the Buddha should not even believe what the Buddha has spoken but to only believe what is experienced for oneself. 

"Knowing thus and seeing thus, would you say, 'The Teacher is our
  respected mentor. We speak thus out of respect for the Teacher'?"
"No, lord."
"Knowing thus and seeing thus, would you say, 'The Contemplative says
  this. We speak thus in line with the Contemplative's words'?"
"No, lord."
"Is it the case that you speak simply in line with what you have
  known, seen, & understood for yourselves?"
"Yes, lord."
"Good, monks. You have been guided by me in this Dhamma which is to be
  seen here & now, timeless, inviting verification, pertinent, to be
  realized by the observant for themselves".
MN 38

There are scriptures where the planes of existence are metaphors so you need to decide for yourself whether 'heaven', 'hell', 'animal behaviour', 'hungry ghosts' & 'humane beings' are metaphors or not. 
Below are quotes that use the term 'animal' obviously as a metaphor: 

Monks, these two bright qualities guard the world. Which two?
  Conscience & concern. If these two bright qualities did not guard the
  world, there would be no recognition of 'mother' here, no recognition
  of 'mother's sister,' 'uncle's wife,' 'teacher's wife,' or 'wife of
  those who deserve respect.' The world would be immersed in
  promiscuity, like rams with goats, roosters with pigs, or dogs with
  jackals. But because these two bright qualities guard the world, there
  is recognition of 'mother,' 'mother's sister,' 'uncle's wife,'
  'teacher's wife' & 'wife of those who deserve respect.'
Lokapala Sutta

~~~


I heard thus. At one time the Blessed One was living in the monastery offered by Anāthapiṇḍika in Jeta's grove in Sāvatthi.
Then a certain monk approached the Blessed One, worshipped, and sat on a side.
Sitting, that monk said to the Blessed One: “Venerable sir, how is it that a certain serpent [snake], born from a womb, observing the full moon
  observances, would even give up his body?”
“Here, monk, to a certain serpent born from a womb it occurs: `Earlier we acted in two ways by body, speech, and mind, and after
  death were born with the serpents born from a womb.'
“`Today we develop the right conduct by body, speech, and mind. In this manner we go to a good state, go to heaven after death.'
“`Therefore at this time we develop the right conduct by body speech and mind.'
“Monk, this is the reason that a certain serpent, born from a womb, observing the full moon observances, would even give up his body.”

Nāga Saṃyutta

~~~

So too, bhikkhus, those beings are few who, when they pass away from
  the animal realm, are reborn among human beings. But those beings are
  more numerous who, when they pass away from the animal realm, are
  reborn in hell.
For what reason? Because bhikkhus, they have not seen the Four Noble
  Truths. What four? The noble truth of suffering, the noble truth of
  the origin of suffering, the noble truth of the cessation of
  suffering, the noble truth of the way leading to the cessation of
  suffering.
SN 56.121 (no link)

~~~

I have heard that on one occasion the Blessed One was staying in
  Savatthi at Jeta's Grove, Anathapindika's monastery. Now at that time
  a large number of monks, after the meal, on returning from their alms
  round, had gathered at the meeting hall and were engaged in many kinds
  of animal topics of conversation: conversation about kings, robbers,
  & ministers of state; armies, alarms, & battles; food & drink;
  clothing, furniture, garlands, & scents; relatives; vehicles;
  villages, towns, cities, the countryside; women & heroes; the gossip
  of the street & the well; tales of the dead; tales of diversity, the
  creation of the world & of the sea; talk of whether things exist or
  not.

AN
    10.70


Watching this whole video carefully about how Angulimala becomes an animal (murderer) then become a human being again (after being reformed by the Buddha) may also help: https://www.youtube.com/watch?v=WBkprM2JJQk

For the 'heavenly realms', MN 1 is useful. MN 1 describes the 1st, 2nd, 3rd & 4th meditative absorptions (jhana) as various heavenly or godly states. 

The Blessed One said: "There is the case, monks, where an uninstructed
  run-of-the-mill person — who has no regard for noble ones, is not
  well-versed or disciplined in their Dhamma; who has no regard for men
  of integrity, is not well-versed or disciplined in their Dhamma —
  perceives earth as earth. Perceiving earth as earth, he conceives
  [things] about earth, he conceives [things] in earth, he conceives
  [things] coming out of earth, he conceives earth as 'mine,' he
  delights in earth. Why is that? Because he has not comprehended it, I
  tell you.
"He perceives water as water... fire as fire... wind as wind ...
  beings as beings... gods as gods...Pajapati as Pajapati...Brahma as
  Brahma... the luminous gods as luminous gods... the gods of refulgent
  glory as gods of refulgent glory... the gods of abundant fruit as the
  gods of abundant fruit... the Conqueror as the Conqueror ... the
  dimension of the infinitude of space as the dimension of the
  infinitude of space... the dimension of the infinitude of
  consciousness as the dimension of the infinitude of consciousness...
  the dimension of nothingness as the dimension of nothingness... the
  dimension of neither-perception-nor-non-perception as the dimension of
  neither-perception-nor-non-perception ... the seen as the seen... the
  heard as the heard... the sensed as the sensed... the cognized as the
  cognized ... singleness as singleness... multiplicity as multiplicity
  ... the All as the All ...
"He perceives Nibbana as Nibbana. Perceiving Nibbana as Nibbana, he
  conceives things about Nibbana, he conceives things in Nibbana, he
  conceives things coming out of Nibbana, he conceives Nibbanaas 'mine,'
  he delights in Nibbana. Why is that? Because he has not comprehended
  it, I tell you.

In MN 79, the jhanas are also described as a "world" ("loka") of pleasant feelings. Here, the word "world" is used to described a mental state, similar to many suttas such as SN 12.44 & AN 4.45, which refer to the "world of suffering". 

Kiṃ panudāyi, atthi ekantasukho loko, atthi ākāravatī paṭipadā
  ekantasukhassa lokassa sacchikiriyāyā
Udayi, is there a world of only pleasantness? Is there a course of
  actions to realise that world of only pleasantness?
Here, Udayi, the bhikkhu secluded from sensual desires and thoughts of
  demerit abides in the first jhana: Overcoming thoughts and thought
  processs and the mind in one point internally appeased, without
  thoughts and thought processes abides in the second jhana. Again with
  equanimuity to joy and detachment, feeling pleasant with the body too,
  abides in the third jhana. To this the noble ones say abiding in
  pleasantness with equanimity. Udayi, this is the course of actions,
  for realising the world of only pleasant feelings (ekantasukhassa
  lokassa).

In MN 75, is discussed the Buddha's former life in the palace before he was monk. Here, the words "divine sensual pleasures" are used to describe the luxurious sensual pleasures of the rich & wealthy. Obviously, the heaven mentioned here (which was also understood by the non-Buddhist questioner) is not a heaven gained from doing good charitable deeds but a heaven of luxurious sensual pleasures:

Māgandiya, formerly when I lived the home life, I enjoyed myself,
  provided and endowed with the five cords of sensual pleasure: with
  forms cognizable by the eye…with sounds cognizable by the ear…with
  odours cognizable by the nose…with flavours cognizable by the
  tongue…with tangibles cognizable by the body that are wished for,
  desired, agreeable, and likeable, connected with sensual desire and
  provocative of lust. I had three palaces, one for the rainy season,
  one for the winter, and one for the summer. I lived in the rains’
  palace for the four months of the rainy season, enjoying myself with
  musicians, none of whom were men, and I did not go down to the lower
  palace.
“On a later occasion, having understood as they actually are the
  origin, the disappearance, the gratification, the danger, and the
  escape in the case of sensual pleasures, I abandoned craving for
  sensual pleasures, I removed fever for sensual pleasures, and I abide
  without thirst, with a mind inwardly at peace. I see other beings who
  are not free from lust for sensual pleasures being devoured by craving
  for sensual pleasures, burning with fever for sensual pleasures,
  indulging in sensual pleasures, and I do not envy them, nor do I
  delight therein. Why is that? Because there is, Māgandiya, a delight [i.e. meditative jhana]
  apart from sensual pleasures, apart from unwholesome states, which
  surpasses even divine bliss. Since I take delight in that, I do not
  envy what is inferior, nor do I delight therein.
“Suppose, Māgandiya, a householder or a householder’s son was rich,
  with great wealth and property, and being provided and endowed with
  the five cords of sensual pleasure, he might enjoy himself with forms
  cognizable by the eye…with sounds cognizable by the ear…with odours
  cognizable by the nose…with flavours cognizable by the tongue…with
  tangibles cognizable by the body that are wished for, desired,
  agreeable, and likeable, connected with sensual desire and provocative
  of lust. Having conducted himself well in body, speech, and mind, on
  the dissolution of the body, after death, he might reappear in a happy
  destination, in the heavenly world in the retinue of the gods of the
  Thirty-three; and there, surrounded by a group of nymphs in the
  Nandana Grove, he would enjoy himself, provided and endowed with the
  five cords of divine sensual pleasure. Suppose he saw a householder or
  a householder’s son enjoying himself, provided and endowed with the
  five cords of human sensual pleasure. What do you think, Māgandiya?
  Would that young god surrounded by the group of nymphs in the Nandana
  Grove, enjoying himself, provided and endowed with the five cords of
  divine sensual pleasure, envy the householder or the householder’s son
  for the five cords of human sensual pleasure or would he be enticed by
  human sensual pleasures?”
“No, Master Gotama. Why not? Because divine sensual pleasures are more
  excellent and sublime than human sensual pleasures.”

In MN 37, Sakka, ruler of the Gods, lives in an actual palace, with rooms & many young sexy young women. If the godly realm here was a literal 'heaven' (in the clouds), why would there be a palace, with rooms? 

Good sir Moggallana, it once happened that war broke our between the
  gods and the titans. In that war the gods won and the titans were
  defeated. When I had won that war and returned from it as a conqueror,
  I had the Vejayanta Palace Built. Good sir Moggallana, the Vejayanta
  Palace has a hundred towers, and each tower has seven hundred upper
  chambers, and each tower has seven nymphs and each nymph has seven
  maids. Would you like to see the loveliness of the Vejayanta Palace,
  good sir Moggallana?"

In SN 11.5, the 'democrat' gods (deva) & 'totalitarian' titans (asura) have a debate about how to rule people. The gods suggest patience & the titans suggest punishment. If gods is a heavenly place & the titans is hellish state of deprivation, how could the gods & titans have a debate with eachother about ruling the world of ordinary people? 
Obviously, the 'gods' here refers to benevolent rulers & the 'titans' refer to tyrannical rulers of the human world who engaged in ideological & often military battle with eachother. 

In summary, the word 'human' ('manussa') in Pali literally means to be 'high minded'. Therefore, it does not refer to 'people' ('puggalo') but to a state of mind. 
When the scripture states: "there is this world & the other worlds", the term "this world" refers to the high virtuous human state of mind when having an audience with a Buddha or noble being. (It does not refer to the planet Earth).
MN 12 distinguishes between types of physical birth & forms of spontaneous mental birth: 


"Sariputta, there are these four kinds of generation. What are the four? Egg-born generation, womb-born generation, moisture-born
  generation and spontaneous generation.
"What is egg-born generation? There are these beings born by breaking out of the shell of an egg; this is called egg-born
  generation. What is womb-born generation? There are these beings born
  by breaking out from the caul; this is called womb-born generation.
  What is moisture-born generation? There are these beings born in a
  rotten fish, in a rotten corpse, in rotten dough, in a cesspit, or in
  a sewer; this is called moisture-born generation. What is spontaneous
  generation? There are gods and denizens of hell and certain human
  beings and some beings in the lower worlds; this is called spontaneous
  generation. These are the four kinds of generation.



user8664: Are the planes of existence real or metaphor? They are both.

user254: Here's my personal interpretation.
A belief in hell, devas, and rebirth preceded (existed before) Buddhism and the Buddha. So when the Buddha was born, lived, and taught, people (non-Buddhists) already had a belief in hell, devas, rebirth, etc.
According to the page you referenced (see also Wikipedia's Buddhist cosmology of the Theravada school) there isn't any one source e.g. a single sutta which identifies the 31 planes ... instead commentators have collected the 31 planes from several sources.
For example one of the suttas, which mentions the arupa-loka, is the Saleyyaka Sutta (MN 41). This starts as follows:


The brahman householders of Sala went to the Blessed One; etc.

When they were seated, they said to the Blessed One: "Master Gotama, what is the reason, what is the condition, why some beings here, on the dissolution of the body, after death, reappear in states of deprivation, in an unhappy destination, in perdition, even in hell; and what is the reason, what is the condition, why some beings here, on the dissolution of the body, after death, reappear in a happy destination, even in the heavenly world?"



In other words, the brahman householders open the discussion by asking, "Why are some people reborn in hell and some in heaven?"
Note that the question assumes/presumes the existence of heaven and hell.
In reply, the Buddha teaches them Dhamma: he defines or gives examples of good and bad bodily conduct, verbal conduct, mental conduct.
Incidentally, the sutta's message ends by saying that "deliverance here and now" is also possible (and is implicitly better than a heavenly rebirth):


"If a householder who observes conduct in accordance with the Dhamma, righteous conduct, should wish: 'Oh, that by realization myself with direct knowledge, I may here and now enter upon and abide in the deliverance of the heart and the deliverance by wisdom that are taint-free with exhaustion of taints!' it is possible that, by realization himself with direct knowledge, he may here and now enter upon and abide in the deliverance of the heart and the deliverance by wisdom that are taint-free with exhaustion of taints. Why is that? Because he observes conduct in accordance with the Dhamma, righteous conduct."


My personal opinion is that the purpose or intent of this sutta, is not to teach us about the various kinds of Gods (though it does list various kinds), rather it is to teach examples of good and bad conduct, and teach that each person's future (destination) depends on their conduct. Whether or not that's really the "sutta's intent", that's what I get out of it when I read it using my personal set of biases.
I see it as being similar to verse 393 of the Dhammapada, i.e. the Buddha uses the existing belief and vocubulary (e.g. the word "brahmin"), he redefines those words, and he reuses their language and belief-system to speak to people (who have pre-existing beliefs).
In other words I think that people of his day believed in rebirth, heaven, and hell, and he used that as a "hook" to tell them about good conduct, e.g. to say that their destination depended on their own behaviour.
I think you can see other examples where the Buddha selects his message to match the audience. When talking to a lay audience, for example, he talked about the six directions; when talking to monks, he talked about renunciation -- different messages to suit different audiences.

I think that a belief in or a doctrine of rebirth is tightly integrated into the Pali canon, for example a literal interpretation of the Four stages of enlightenment including "once-returner" and "non-returner" presume rebirth and rebirth in heaven.
IMO trying to remove a belief in "planes of existence" from Theravada might be like trying to remove a belief in "heaven" from Christianity i.e. it's not easy or a natural way to interpret the scripture.

One way to answer this is to say that, inline with the reasoning I gave in this answer, it might be useful to behave as if the realms exist, i.e. behave as if our conduct has future consequence.

Also, so far as I know, an orthodox answer from a Theravadin (i.e. a type of answer that I have seen from other users on this site) might be that you should practice to perfect yourself and your spiritual abilities until you can know/see the truth for yourself.

2225: <p>And How the buddha know all of these things. I suppose he knew from meditation until enlighten? So it is possible that just by mediation alone one can know about other realm of existence.</p>

<p><a href="http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html" rel="nofollow">http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html</a></p>
 8157: <p>There is a major principle in original Buddhism that the Dhamma (true reality) is experienced in the here-&amp;-now (<em>sanditthiko</em>); has immediate results (<em>akaliko</em>); invites inspection (<em>ehipassiko</em>); leads to peace (<em>opanayiko</em>); &amp; verified by the observant for themselves (<em>paccattam veditabbo vinnuhi</em>).  </p>

<p>MN 38 states disciples of the Buddha should not even believe what the Buddha has spoken but to only believe what is experienced for oneself. </p>

<blockquote>
  <p>"Knowing thus and seeing thus, would you say, 'The Teacher is our
  respected mentor. We speak thus out of respect for the Teacher'?"</p>
  
  <p>"No, lord."</p>
  
  <p>"Knowing thus and seeing thus, would you say, 'The Contemplative says
  this. We speak thus in line with the Contemplative's words'?"</p>
  
  <p>"No, lord."</p>
  
  <p>"Is it the case that you speak simply in line with what you have
  known, seen, &amp; understood for yourselves?"</p>
  
  <p>"Yes, lord."</p>
  
  <p>"Good, monks. You have been guided by me in this Dhamma which is to be
  seen here &amp; now, timeless, inviting verification, pertinent, to be
  realized by the observant for themselves".</p>
  
  <p><a href="http://www.accesstoinsight.org/tipitaka/mn/mn.038.than.html" rel="nofollow">MN 38</a></p>
</blockquote>

<p>There are scriptures where the planes of existence are metaphors so you need to decide for yourself whether 'heaven', 'hell', 'animal behaviour', 'hungry ghosts' &amp; 'humane beings' are metaphors or not. </p>

<p>Below are quotes that use the term '<strong>animal</strong>' obviously as a metaphor: </p>

<blockquote>
  <p>Monks, these two bright qualities guard the world. Which two?
  Conscience &amp; concern. If these two bright qualities did not guard the
  world, there would be no recognition of 'mother' here, no recognition
  of 'mother's sister,' 'uncle's wife,' 'teacher's wife,' or 'wife of
  those who deserve respect.' The world would be immersed in
  promiscuity, like rams with <strong>goats</strong>, roosters with <strong>pigs</strong>, or dogs with
  <strong>jackals</strong>. But because these two bright qualities guard the world, there
  is recognition of 'mother,' 'mother's sister,' 'uncle's wife,'
  'teacher's wife' &amp; 'wife of those who deserve respect.'</p>
  
  <p><a href="http://www.accesstoinsight.org/tipitaka/an/an02/an02.009.than.html" rel="nofollow">Lokapala Sutta</a></p>
</blockquote>

<p>~~~</p>

<blockquote>
  <ol>
  <li><p>I heard thus. At one time the Blessed One was living in the monastery offered by Anāthapiṇḍika in Jeta's grove in Sāvatthi.</p></li>
  <li><p>Then a certain monk approached the Blessed One, worshipped, and sat on a side.</p></li>
  <li><p>Sitting, that monk said to the Blessed One: “Venerable sir, how is it that a certain <strong>serpent</strong> [snake], born from a womb, observing the full moon
  observances, would even give up his body?”</p></li>
  <li><p>“Here, monk, to a certain serpent born from a womb it occurs: `Earlier we acted in two ways by body, speech, and mind, and after
  death were born with the serpents born from a womb.'</p></li>
  <li><p>“`Today we develop the right conduct by body, speech, and mind. In this manner we go to a good state, go to heaven after death.'</p></li>
  <li><p>“`Therefore at this time we develop the right conduct by body speech and mind.'</p></li>
  <li><p>“Monk, this is the reason that a certain serpent, born from a womb, observing the full moon observances, would even give up his body.”</p></li>
  </ol>
  
  <p><a href="http://awake.kiev.ua/dhamma/tipitaka/2Sutta-Pitaka/3Samyutta-Nikaya/Samyutta3/28-Naga-Samyutta/01-Nagavaggo-e.html" rel="nofollow">Nāga Saṃyutta</a></p>
</blockquote>

<p>~~~</p>

<blockquote>
  <p>So too, bhikkhus, those beings are <strong>few</strong> who, when they pass away from
  the <strong>animal realm</strong>, are reborn among human beings. But those beings are
  more numerous who, when they pass away from the animal realm, are
  reborn in hell.</p>
  
  <p>For what reason? Because bhikkhus, they have not <strong>seen the Four Noble
  Truths</strong>. What four? The noble truth of suffering, the noble truth of
  the origin of suffering, the noble truth of the cessation of
  suffering, the noble truth of the way leading to the cessation of
  suffering.</p>
  
  <p>SN 56.121 (no link)</p>
</blockquote>

<p>~~~</p>

<blockquote>
  <p>I have heard that on one occasion the Blessed One was staying in
  Savatthi at Jeta's Grove, Anathapindika's monastery. Now at that time
  a large number of monks, after the meal, on returning from their alms
  round, had gathered at the meeting hall and were engaged in many kinds
  of <strong>animal</strong> topics of conversation: conversation about kings, robbers,
  &amp; ministers of state; armies, alarms, &amp; battles; food &amp; drink;
  clothing, furniture, garlands, &amp; scents; relatives; vehicles;
  villages, towns, cities, the countryside; women &amp; heroes; the gossip
  of the street &amp; the well; tales of the dead; tales of diversity, the
  creation of the world &amp; of the sea; talk of whether things exist or
  not.</p>
  
  <blockquote>
    <p><a href="http://www.accesstoinsight.org/tipitaka/an/an10/an10.070.than.html" rel="nofollow">AN
    10.70</a></p>
  </blockquote>
</blockquote>

<p>Watching this whole video carefully about how Angulimala becomes an animal (murderer) then become a human being again (after being reformed by the Buddha) may also help: <a href="https://www.youtube.com/watch?v=WBkprM2JJQk" rel="nofollow">https://www.youtube.com/watch?v=WBkprM2JJQk</a></p>

<hr>

<p>For the '<strong>heavenly realms</strong>', <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.001.than.html" rel="nofollow">MN 1</a> is useful. <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.001.than.html" rel="nofollow">MN 1</a> describes the 1st, 2nd, 3rd &amp; 4th meditative absorptions (<strong>jhana</strong>) as various heavenly or godly states. </p>

<blockquote>
  <p>The Blessed One said: "There is the case, monks, where an uninstructed
  run-of-the-mill person — who has no regard for noble ones, is not
  well-versed or disciplined in their Dhamma; who has no regard for men
  of integrity, is not well-versed or disciplined in their Dhamma —
  perceives earth as earth. Perceiving earth as earth, he conceives
  [things] about earth, he conceives [things] in earth, he conceives
  [things] coming out of earth, he conceives earth as 'mine,' he
  delights in earth. Why is that? Because he has not comprehended it, I
  tell you.</p>
  
  <p>"He perceives water as water... fire as fire... wind as wind ...
  beings as beings... gods as gods...Pajapati as Pajapati...Brahma as
  Brahma... the <strong>luminous gods</strong> as luminous gods... the <strong>gods of refulgent
  glory</strong> as gods of refulgent glory... the <strong>gods of abundant fruit</strong> as the
  gods of abundant fruit... the <strong>Conqueror</strong> as the Conqueror ... the
  dimension of the infinitude of space as the dimension of the
  infinitude of space... the dimension of the infinitude of
  consciousness as the dimension of the infinitude of consciousness...
  the dimension of nothingness as the dimension of nothingness... the
  dimension of neither-perception-nor-non-perception as the dimension of
  neither-perception-nor-non-perception ... the seen as the seen... the
  heard as the heard... the sensed as the sensed... the cognized as the
  cognized ... singleness as singleness... multiplicity as multiplicity
  ... the All as the All ...</p>
  
  <p>"He perceives Nibbana as Nibbana. Perceiving Nibbana as Nibbana, he
  conceives things about Nibbana, he conceives things in Nibbana, he
  conceives things coming out of Nibbana, he conceives Nibbanaas 'mine,'
  he delights in Nibbana. Why is that? Because he has not comprehended
  it, I tell you.</p>
</blockquote>

<p>In <a href="http://www.vipassana.info/079-culasakuludayi-e1.htm" rel="nofollow">MN 79</a>, the jhanas are also described as a "world" ("loka") of pleasant feelings. Here, the word "world" is used to described a mental state, similar to many suttas such as SN 12.44 &amp; AN 4.45, which refer to the "world of suffering". </p>

<blockquote>
  <p>Kiṃ panudāyi, atthi ekantasukho loko, atthi ākāravatī paṭipadā
  ekantasukhassa lokassa sacchikiriyāyā</p>
  
  <p>Udayi, is there a world of only pleasantness? Is there a course of
  actions to realise that <strong>world of only pleasantness</strong>?</p>
  
  <p>Here, Udayi, the bhikkhu secluded from sensual desires and thoughts of
  demerit abides in the first jhana: Overcoming thoughts and thought
  processs and the mind in one point internally appeased, without
  thoughts and thought processes abides in the second jhana. Again with
  equanimuity to joy and detachment, feeling pleasant with the body too,
  abides in the third jhana. To this the noble ones say abiding in
  pleasantness with equanimity. Udayi, this is the course of actions,
  for realising the world of only pleasant feelings (ekantasukhassa
  lokassa).</p>
</blockquote>

<p>In <a href="https://suttacentral.net/en/mn75" rel="nofollow">MN 75</a>, is discussed the Buddha's former life in the palace before he was monk. Here, the words "divine sensual pleasures" are used to describe the luxurious sensual pleasures of the rich &amp; wealthy. Obviously, the heaven mentioned here (which was also understood by the non-Buddhist questioner) is not a heaven gained from doing good charitable deeds but a heaven of luxurious sensual pleasures:</p>

<blockquote>
  <p>Māgandiya, formerly when I lived the home life, I enjoyed myself,
  provided and endowed with the five cords of sensual pleasure: with
  forms cognizable by the eye…with sounds cognizable by the ear…with
  odours cognizable by the nose…with flavours cognizable by the
  tongue…with tangibles cognizable by the body that are wished for,
  desired, agreeable, and likeable, connected with sensual desire and
  provocative of lust. I had three palaces, one for the rainy season,
  one for the winter, and one for the summer. I lived in the rains’
  palace for the four months of the rainy season, enjoying myself with
  musicians, none of whom were men, and I did not go down to the lower
  palace.</p>
  
  <p>“On a later occasion, having understood as they actually are the
  origin, the disappearance, the gratification, the danger, and the
  escape in the case of sensual pleasures, I abandoned craving for
  sensual pleasures, I removed fever for sensual pleasures, and I abide
  without thirst, with a mind inwardly at peace. I see other beings who
  are not free from lust for sensual pleasures being devoured by craving
  for sensual pleasures, burning with fever for sensual pleasures,
  indulging in sensual pleasures, and I do not envy them, nor do I
  delight therein. Why is that? Because <strong>there is, Māgandiya, a delight [i.e. meditative jhana]
  apart from sensual pleasures, apart from unwholesome states, which
  surpasses even divine bliss</strong>. Since I take delight in that, I do not
  envy what is inferior, nor do I delight therein.</p>
  
  <p>“Suppose, Māgandiya, a householder or a householder’s son was rich,
  with great wealth and property, and being provided and endowed with
  the five cords of sensual pleasure, he might enjoy himself with forms
  cognizable by the eye…with sounds cognizable by the ear…with odours
  cognizable by the nose…with flavours cognizable by the tongue…with
  tangibles cognizable by the body that are wished for, desired,
  agreeable, and likeable, connected with sensual desire and provocative
  of lust. Having conducted himself well in body, speech, and mind, on
  the dissolution of the body, after death, he might reappear in a happy
  destination, in the heavenly world in the retinue of the gods of the
  Thirty-three; and there, surrounded by a group of nymphs in the
  Nandana Grove, he would enjoy himself, provided and endowed with the
  five cords of divine sensual pleasure. Suppose he saw a householder or
  a householder’s son enjoying himself, provided and endowed with the
  five cords of human sensual pleasure. What do you think, Māgandiya?
  Would that young god surrounded by the group of nymphs in the Nandana
  Grove, enjoying himself, provided and endowed with the five cords of
  divine sensual pleasure, envy the householder or the householder’s son
  for the five cords of human sensual pleasure or would he be enticed by
  human sensual pleasures?”</p>
  
  <p>“No, Master Gotama. Why not? Because divine sensual pleasures are more
  excellent and sublime than human sensual pleasures.”</p>
</blockquote>

<p>In <a href="http://www.dhammatalks.net/Books9/Bhikkhu_Bodhi_Culatanhasankhaya_Sutta.htm" rel="nofollow">MN 37</a>, Sakka, ruler of the Gods, lives in an actual palace, with rooms &amp; many young sexy young women. If the godly realm here was a literal 'heaven' (in the clouds), why would there be a palace, with rooms? </p>

<blockquote>
  <p>Good sir Moggallana, it once happened that war broke our between the
  gods and the titans. In that war the gods won and the titans were
  defeated. When I had won that war and returned from it as a conqueror,
  I had the Vejayanta Palace Built. Good sir Moggallana, the Vejayanta
  Palace has a hundred towers, and each tower has seven hundred upper
  chambers, and each tower has seven nymphs and each nymph has seven
  maids. Would you like to see the loveliness of the Vejayanta Palace,
  good sir Moggallana?"</p>
</blockquote>

<p>In <a href="http://www.accesstoinsight.org/tipitaka/sn/sn11/sn11.005.than.html" rel="nofollow">SN 11.5</a>, the 'democrat' gods (deva) &amp; 'totalitarian' titans (asura) have a debate about how to rule people. The gods suggest patience &amp; the titans suggest punishment. If gods is a heavenly place &amp; the titans is hellish state of deprivation, how could the gods &amp; titans have a debate with eachother about ruling the world of ordinary people? </p>

<p>Obviously, the 'gods' here refers to benevolent rulers &amp; the 'titans' refer to tyrannical rulers of the human world who engaged in ideological &amp; often military battle with eachother. </p>

<hr>

<p>In summary, the word '<strong>human</strong>' ('manussa') in Pali literally means to be 'high minded'. Therefore, it does not refer to 'people' ('puggalo') but to a state of mind. </p>

<p>When the scripture states: "there is this world &amp; the other worlds", the term "this world" refers to the high virtuous human state of mind when having an audience with a Buddha or noble being. (It does not refer to the planet Earth).</p>

<p><a href="http://www.accesstoinsight.org/tipitaka/mn/mn.012.ntbb.html" rel="nofollow">MN 12</a> distinguishes between types of physical birth &amp; forms of spontaneous mental birth: </p>

<blockquote>
  <ol start="32">
  <li><p>"Sariputta, there are these four kinds of generation. What are the four? Egg-born generation, womb-born generation, moisture-born
  generation and spontaneous generation.</p></li>
  <li><p>"What is egg-born generation? There are these beings born by breaking out of the shell of an egg; this is called egg-born
  generation. What is womb-born generation? There are these beings born
  by breaking out from the caul; this is called womb-born generation.
  What is moisture-born generation? There are these beings born in a
  rotten fish, in a rotten corpse, in rotten dough, in a cesspit, or in
  a sewer; this is called moisture-born generation. What is spontaneous
  generation? There are gods and denizens of hell and certain human
  beings and some beings in the lower worlds; this is called spontaneous
  generation. These are the four kinds of generation.</p></li>
  </ol>
</blockquote>
 8664: <p>Are the planes of existence real or metaphor? They are both.</p>
 254: <p>Here's my personal interpretation.</p>
<p>A belief in hell, devas, and rebirth preceded (existed before) Buddhism and the Buddha. So when the Buddha was born, lived, and taught, people (non-Buddhists) already had a belief in hell, devas, rebirth, etc.</p>
<p>According to the page you referenced (see also Wikipedia's <a href="https://en.wikipedia.org/wiki/Buddhist_cosmology_of_the_Theravada_school" rel="nofollow noreferrer">Buddhist cosmology of the Theravada school</a>) there isn't any one source e.g. a single sutta which identifies the 31 planes ... instead commentators have collected the 31 planes from several sources.</p>
<p>For example one of the suttas, which mentions the <em>arupa-loka</em>, is the <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.041.nymo.html" rel="nofollow noreferrer">Saleyyaka Sutta (MN 41)</a>. This starts as follows:</p>
<blockquote>
<ol start="3">
<li><p>The brahman householders of Sala went to the Blessed One; etc.</p>
</li>
<li><p>When they were seated, they said to the Blessed One: &quot;Master Gotama, what is the reason, what is the condition, why some beings here, on the dissolution of the body, after death, reappear in states of deprivation, in an unhappy destination, in perdition, even in hell; and what is the reason, what is the condition, why some beings here, on the dissolution of the body, after death, reappear in a happy destination, even in the heavenly world?&quot;</p>
</li>
</ol>
</blockquote>
<p>In other words, the brahman householders open the discussion by asking, &quot;Why are some people reborn in hell and some in heaven?&quot;</p>
<p>Note that the question assumes/presumes the existence of heaven and hell.</p>
<p>In reply, the Buddha teaches them Dhamma: he defines or gives examples of good and bad bodily conduct, verbal conduct, mental conduct.</p>
<p>Incidentally, the sutta's message ends by saying that &quot;deliverance here and now&quot; is also possible (and is implicitly better than a heavenly rebirth):</p>
<blockquote>
<ol start="43">
<li>&quot;If a householder who observes conduct in accordance with the Dhamma, righteous conduct, should wish: 'Oh, that by realization myself with direct knowledge, I may here and now enter upon and abide in the deliverance of the heart and the deliverance by wisdom that are taint-free with exhaustion of taints!' it is possible that, by realization himself with direct knowledge, he may here and now enter upon and abide in the deliverance of the heart and the deliverance by wisdom that are taint-free with exhaustion of taints. Why is that? Because he observes conduct in accordance with the Dhamma, righteous conduct.&quot;</li>
</ol>
</blockquote>
<p>My personal opinion is that the purpose or intent of this sutta, is not to teach us about the various kinds of Gods (though it does list various kinds), rather it <em>is</em> to teach <em>examples</em> of good and bad conduct, and teach that each person's future (destination) depends on their conduct. Whether or not that's really the &quot;sutta's intent&quot;, that's what I get out of it when I read it using my personal set of biases.</p>
<p>I see it as being similar to <a href="http://www.tipitaka.net/tipitaka/dhp/verseload.php?verse=393" rel="nofollow noreferrer">verse 393 of the Dhammapada</a>, i.e. the Buddha uses the existing belief and vocubulary (e.g. the word &quot;brahmin&quot;), he <em>redefines</em> those words, and he reuses their language and belief-system to speak to people (who have pre-existing beliefs).</p>
<p>In other words I think that people of his day believed in rebirth, heaven, and hell, and he used that as a &quot;<a href="https://en.wikipedia.org/wiki/Narrative_hook" rel="nofollow noreferrer">hook</a>&quot; to tell them about good conduct, e.g. to say that their destination depended on their own behaviour.</p>
<p>I think you can see other examples where the Buddha selects his message to match the audience. When talking to a lay audience, for example, he talked about the six directions; when talking to monks, he talked about renunciation -- different messages to suit different audiences.</p>
<hr />
<p>I think that a belief in or a doctrine of rebirth is tightly integrated into the Pali canon, for example a literal interpretation of the <a href="https://en.wikipedia.org/wiki/Four_stages_of_enlightenment" rel="nofollow noreferrer">Four stages of enlightenment</a> including &quot;once-returner&quot; and &quot;non-returner&quot; presume rebirth and rebirth in heaven.</p>
<p>IMO trying to remove a belief in &quot;planes of existence&quot; from Theravada might be like trying to remove a belief in &quot;heaven&quot; from Christianity i.e. it's not easy or a natural way to interpret the scripture.</p>
<hr />
<p>One way to answer this is to say that, inline with the reasoning I gave in <a href="https://buddhism.stackexchange.com/a/15654/254">this answer</a>, it might be useful to <em>behave as if</em> the realms exist, i.e. behave as if our conduct has future consequence.</p>
<hr />
<p>Also, so far as I know, an orthodox answer from a Theravadin (i.e. a type of answer that I have seen from other users on this site) might be that you should practice to perfect yourself and your spiritual abilities until you can know/see the truth for yourself.</p>
