Describing the size of Paradise as being “as wide as the heavens and the earth”
Question

Allah describes the width of Paradise as being like the width of the heavens and the earth. My question is: it is well known that the heaven is much, much bigger than the earth. So what is the point of including the earth in this description?
For example, it is like saying that the size of Russia is bigger than Saudi and Riyadh. What is the point of including Riyadh in this description when it does not add anything to the meaning, because Riyadh is part of Saudi?
Praise be to Allah.Allah, may He be exalted, says (interpretation of the meaning):
“And march forth in the way (which leads to) forgiveness from your Lord, and for Paradise as wide as are the heavens and the earth, prepared for Al-Muttaqoon (the pious)”
[Aal ‘Imraan 3:133]
“Race with one another in hastening towards forgiveness from your Lord (Allah), and Paradise the width whereof is as the width of the heaven and the earth, prepared for those who believe in Allah and His Messengers”
[al-Hadeed 57:21].
Al-Qurtubi (may Allah have mercy on him) said:
The scholars differed concerning the interpretation of that. Ibn ‘Abbaas said: It is as if the heavens and the earth are put together and joined together, like garments spread out and attached to one another. That is the width of Paradise, and no one knows its length except Allah. This is the view of the majority, and it is nothing strange.
Some scholars said: This is a metaphor that may be used by the Arabs. As Paradise is so big and vast, in the utmost sense, it is appropriate to refer to its size by mentioning the width of the heavens and the earth. By the same token, one may describe a man (in Arabic) as being a “sea” (bahr – referring to the vastness of his knowledge, for example), and one may describe a huge animal as being a “mountain.” The verse is not intended to specify its precise width; rather what is meant is that it is like the biggest size you have ever seen.
End quote from Tafseer al-Qurtubi (4/204-205).
Ibn ‘Aashoor (may Allah have mercy on him) said:
The heavens and the earth are mentioned by way of metaphor, in the Arabic manner of describing how vast something is. It does not mean precisely how wide the heavens and the earth are. And it was said that it refers to the actual width of paradise; it is created now, but it is bigger than the heavens, and it is above the heavens, beneath the Throne. End quote.
Ash-Shawkaani (may Allah have mercy on him) said:
There was a difference of opinion concerning the meaning of that. The majority of scholars are of the view that it as if the heavens and the earth are put together and joined together, like garments spread out and attached to one another, and that is the width of Paradise. The width is mentioned, but not the length, because usually the length is greater than the width.
It was said that this is a metaphor that the Arabs use, and it is not talking about the exact size. As Paradise is so vast and huge, in the utmost sense, it is appropriate to compare it to the width of the heavens and the earth by way of emphasis, because they are the vastest of Allah’s creation that people know. It is not meant literally.
End quote from Fath al-Qadeer (1/437). See also: at-Tahreer wa’t-Tanweer (4/89).
Thus we see that the scholars have two views concerning the interpretation of the verse: the view of the majority, which is that what is meant is the actual width, and its length is implied by that; and the second view, which is that what is meant is to highlight the vastness of Paradise, but it does not refer to its exact length and width – rather it is expressed in accordance with Arabic usage concerning such matters.
Whatever the case, the example given in the question regarding area and size is irrelevant. All the examples given in the question a far removed from the way in which the verse expressed the meaning. You mentioned Riyadh as an example, but it is a part of Saudi, whereas the heavens and the earth are two completely independent entities.
Usually religious texts in such cases describe matters of the unseen in a way that is easy for people to understand and is in accordance with their usual speech and way of expression. Undoubtedly mentioning the earth that they know and see how vast it is, and how far it extends, makes it easier for them to grasp the intended meaning than if it were to be ignored completely. What you must do is realise that the superiority of the words of Allah, may He be glorified and exalted, to the words of human beings is like the superiority of Allah, may He be glorified and exalted, to His creation. The words of Allah are far above any contradictions, faults or falling short of the utmost beauty, majesty and eloquence, which befits the noblest of speech. If a person fails and is unable to understand anything of that, then what he must do is doubt his understanding, his reasoning, his knowledge and his taste, and whatever he does not understand (of the words of Allah), let him refer it to those who know it and trust that there are scholars who have knowledge of that.
And Allah knows best.